1//! Utilities for formatting and printing strings.
2
3#![stable(feature = "rust1", since = "1.0.0")]
4
5use crate::cell::{Cell, Ref, RefCell, RefMut, SyncUnsafeCell, UnsafeCell};
6use crate::char::EscapeDebugExtArgs;
7use crate::iter;
8use crate::marker::PhantomData;
9use crate::mem;
10use crate::num::fmt as numfmt;
11use crate::ops::Deref;
12use crate::result;
13use crate::str;
14
15mod builders;
16#[cfg(not(no_fp_fmt_parse))]
17mod float;
18#[cfg(no_fp_fmt_parse)]
19mod nofloat;
20mod num;
21mod rt;
22
23#[stable(feature = "fmt_flags_align", since = "1.28.0")]
24#[cfg_attr(not(test), rustc_diagnostic_item = "Alignment")]
25/// Possible alignments returned by `Formatter::align`
26#[derive(Copy, Clone, Debug, PartialEq, Eq)]
27pub enum Alignment {
28 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
29 /// Indication that contents should be left-aligned.
30 Left,
31 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
32 /// Indication that contents should be right-aligned.
33 Right,
34 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
35 /// Indication that contents should be center-aligned.
36 Center,
37}
38
39#[stable(feature = "debug_builders", since = "1.2.0")]
40pub use self::builders::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
41
42#[unstable(feature = "debug_closure_helpers", issue = "117729")]
43pub use self::builders::FormatterFn;
44
45/// The type returned by formatter methods.
46///
47/// # Examples
48///
49/// ```
50/// use std::fmt;
51///
52/// #[derive(Debug)]
53/// struct Triangle {
54/// a: f32,
55/// b: f32,
56/// c: f32
57/// }
58///
59/// impl fmt::Display for Triangle {
60/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
61/// write!(f, "({}, {}, {})", self.a, self.b, self.c)
62/// }
63/// }
64///
65/// let pythagorean_triple = Triangle { a: 3.0, b: 4.0, c: 5.0 };
66///
67/// assert_eq!(format!("{pythagorean_triple}"), "(3, 4, 5)");
68/// ```
69#[stable(feature = "rust1", since = "1.0.0")]
70pub type Result = result::Result<(), Error>;
71
72/// The error type which is returned from formatting a message into a stream.
73///
74/// This type does not support transmission of an error other than that an error
75/// occurred. Any extra information must be arranged to be transmitted through
76/// some other means.
77///
78/// An important thing to remember is that the type `fmt::Error` should not be
79/// confused with [`std::io::Error`] or [`std::error::Error`], which you may also
80/// have in scope.
81///
82/// [`std::io::Error`]: ../../std/io/struct.Error.html
83/// [`std::error::Error`]: ../../std/error/trait.Error.html
84///
85/// # Examples
86///
87/// ```rust
88/// use std::fmt::{self, write};
89///
90/// let mut output = String::new();
91/// if let Err(fmt::Error) = write(&mut output, format_args!("Hello {}!", "world")) {
92/// panic!("An error occurred");
93/// }
94/// ```
95#[stable(feature = "rust1", since = "1.0.0")]
96#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
97pub struct Error;
98
99/// A trait for writing or formatting into Unicode-accepting buffers or streams.
100///
101/// This trait only accepts UTF-8–encoded data and is not [flushable]. If you only
102/// want to accept Unicode and you don't need flushing, you should implement this trait;
103/// otherwise you should implement [`std::io::Write`].
104///
105/// [`std::io::Write`]: ../../std/io/trait.Write.html
106/// [flushable]: ../../std/io/trait.Write.html#tymethod.flush
107#[stable(feature = "rust1", since = "1.0.0")]
108pub trait Write {
109 /// Writes a string slice into this writer, returning whether the write
110 /// succeeded.
111 ///
112 /// This method can only succeed if the entire string slice was successfully
113 /// written, and this method will not return until all data has been
114 /// written or an error occurs.
115 ///
116 /// # Errors
117 ///
118 /// This function will return an instance of [`std::fmt::Error`][Error] on error.
119 ///
120 /// The purpose of that error is to abort the formatting operation when the underlying
121 /// destination encounters some error preventing it from accepting more text; it should
122 /// generally be propagated rather than handled, at least when implementing formatting traits.
123 ///
124 /// # Examples
125 ///
126 /// ```
127 /// use std::fmt::{Error, Write};
128 ///
129 /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
130 /// f.write_str(s)
131 /// }
132 ///
133 /// let mut buf = String::new();
134 /// writer(&mut buf, "hola").unwrap();
135 /// assert_eq!(&buf, "hola");
136 /// ```
137 #[stable(feature = "rust1", since = "1.0.0")]
138 fn write_str(&mut self, s: &str) -> Result;
139
140 /// Writes a [`char`] into this writer, returning whether the write succeeded.
141 ///
142 /// A single [`char`] may be encoded as more than one byte.
143 /// This method can only succeed if the entire byte sequence was successfully
144 /// written, and this method will not return until all data has been
145 /// written or an error occurs.
146 ///
147 /// # Errors
148 ///
149 /// This function will return an instance of [`Error`] on error.
150 ///
151 /// # Examples
152 ///
153 /// ```
154 /// use std::fmt::{Error, Write};
155 ///
156 /// fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
157 /// f.write_char(c)
158 /// }
159 ///
160 /// let mut buf = String::new();
161 /// writer(&mut buf, 'a').unwrap();
162 /// writer(&mut buf, 'b').unwrap();
163 /// assert_eq!(&buf, "ab");
164 /// ```
165 #[stable(feature = "fmt_write_char", since = "1.1.0")]
166 fn write_char(&mut self, c: char) -> Result {
167 self.write_str(c.encode_utf8(&mut [0; 4]))
168 }
169
170 /// Glue for usage of the [`write!`] macro with implementors of this trait.
171 ///
172 /// This method should generally not be invoked manually, but rather through
173 /// the [`write!`] macro itself.
174 ///
175 /// # Errors
176 ///
177 /// This function will return an instance of [`Error`] on error. Please see
178 /// [write_str](Write::write_str) for details.
179 ///
180 /// # Examples
181 ///
182 /// ```
183 /// use std::fmt::{Error, Write};
184 ///
185 /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
186 /// f.write_fmt(format_args!("{s}"))
187 /// }
188 ///
189 /// let mut buf = String::new();
190 /// writer(&mut buf, "world").unwrap();
191 /// assert_eq!(&buf, "world");
192 /// ```
193 #[stable(feature = "rust1", since = "1.0.0")]
194 fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
195 // We use a specialization for `Sized` types to avoid an indirection
196 // through `&mut self`
197 trait SpecWriteFmt {
198 fn spec_write_fmt(self, args: Arguments<'_>) -> Result;
199 }
200
201 impl<W: Write + ?Sized> SpecWriteFmt for &mut W {
202 #[inline]
203 default fn spec_write_fmt(mut self, args: Arguments<'_>) -> Result {
204 if let Some(s) = args.as_statically_known_str() {
205 self.write_str(s)
206 } else {
207 write(&mut self, args)
208 }
209 }
210 }
211
212 impl<W: Write> SpecWriteFmt for &mut W {
213 #[inline]
214 fn spec_write_fmt(self, args: Arguments<'_>) -> Result {
215 if let Some(s) = args.as_statically_known_str() {
216 self.write_str(s)
217 } else {
218 write(self, args)
219 }
220 }
221 }
222
223 self.spec_write_fmt(args)
224 }
225}
226
227#[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
228impl<W: Write + ?Sized> Write for &mut W {
229 fn write_str(&mut self, s: &str) -> Result {
230 (**self).write_str(s)
231 }
232
233 fn write_char(&mut self, c: char) -> Result {
234 (**self).write_char(c)
235 }
236
237 fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
238 (**self).write_fmt(args)
239 }
240}
241
242/// Configuration for formatting.
243///
244/// A `Formatter` represents various options related to formatting. Users do not
245/// construct `Formatter`s directly; a mutable reference to one is passed to
246/// the `fmt` method of all formatting traits, like [`Debug`] and [`Display`].
247///
248/// To interact with a `Formatter`, you'll call various methods to change the
249/// various options related to formatting. For examples, please see the
250/// documentation of the methods defined on `Formatter` below.
251#[allow(missing_debug_implementations)]
252#[stable(feature = "rust1", since = "1.0.0")]
253#[rustc_diagnostic_item = "Formatter"]
254pub struct Formatter<'a> {
255 flags: u32,
256 fill: char,
257 align: rt::Alignment,
258 width: Option<usize>,
259 precision: Option<usize>,
260
261 buf: &'a mut (dyn Write + 'a),
262}
263
264impl<'a> Formatter<'a> {
265 /// Creates a new formatter with default settings.
266 ///
267 /// This can be used as a micro-optimization in cases where a full `Arguments`
268 /// structure (as created by `format_args!`) is not necessary; `Arguments`
269 /// is a little more expensive to use in simple formatting scenarios.
270 ///
271 /// Currently not intended for use outside of the standard library.
272 #[unstable(feature = "fmt_internals", reason = "internal to standard library", issue = "none")]
273 #[doc(hidden)]
274 pub fn new(buf: &'a mut (dyn Write + 'a)) -> Formatter<'a> {
275 Formatter {
276 flags: 0,
277 fill: ' ',
278 align: rt::Alignment::Unknown,
279 width: None,
280 precision: None,
281 buf,
282 }
283 }
284}
285
286/// This structure represents a safely precompiled version of a format string
287/// and its arguments. This cannot be generated at runtime because it cannot
288/// safely be done, so no constructors are given and the fields are private
289/// to prevent modification.
290///
291/// The [`format_args!`] macro will safely create an instance of this structure.
292/// The macro validates the format string at compile-time so usage of the
293/// [`write()`] and [`format()`] functions can be safely performed.
294///
295/// You can use the `Arguments<'a>` that [`format_args!`] returns in `Debug`
296/// and `Display` contexts as seen below. The example also shows that `Debug`
297/// and `Display` format to the same thing: the interpolated format string
298/// in `format_args!`.
299///
300/// ```rust
301/// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
302/// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
303/// assert_eq!("1 foo 2", display);
304/// assert_eq!(display, debug);
305/// ```
306///
307/// [`format()`]: ../../std/fmt/fn.format.html
308#[lang = "format_arguments"]
309#[stable(feature = "rust1", since = "1.0.0")]
310#[derive(Copy, Clone)]
311pub struct Arguments<'a> {
312 // Format string pieces to print.
313 pieces: &'a [&'static str],
314
315 // Placeholder specs, or `None` if all specs are default (as in "{}{}").
316 fmt: Option<&'a [rt::Placeholder]>,
317
318 // Dynamic arguments for interpolation, to be interleaved with string
319 // pieces. (Every argument is preceded by a string piece.)
320 args: &'a [rt::Argument<'a>],
321}
322
323/// Used by the format_args!() macro to create a fmt::Arguments object.
324#[doc(hidden)]
325#[unstable(feature = "fmt_internals", issue = "none")]
326impl<'a> Arguments<'a> {
327 #[inline]
328 #[rustc_const_unstable(feature = "const_fmt_arguments_new", issue = "none")]
329 pub const fn new_const(pieces: &'a [&'static str]) -> Self {
330 if pieces.len() > 1 {
331 panic!("invalid args");
332 }
333 Arguments { pieces, fmt: None, args: &[] }
334 }
335
336 /// When using the format_args!() macro, this function is used to generate the
337 /// Arguments structure.
338 #[inline]
339 pub fn new_v1(pieces: &'a [&'static str], args: &'a [rt::Argument<'a>]) -> Arguments<'a> {
340 if pieces.len() < args.len() || pieces.len() > args.len() + 1 {
341 panic!("invalid args");
342 }
343 Arguments { pieces, fmt: None, args }
344 }
345
346 /// This function is used to specify nonstandard formatting parameters.
347 ///
348 /// An `rt::UnsafeArg` is required because the following invariants must be held
349 /// in order for this function to be safe:
350 /// 1. The `pieces` slice must be at least as long as `fmt`.
351 /// 2. Every `rt::Placeholder::position` value within `fmt` must be a valid index of `args`.
352 /// 3. Every `rt::Count::Param` within `fmt` must contain a valid index of `args`.
353 #[inline]
354 pub fn new_v1_formatted(
355 pieces: &'a [&'static str],
356 args: &'a [rt::Argument<'a>],
357 fmt: &'a [rt::Placeholder],
358 _unsafe_arg: rt::UnsafeArg,
359 ) -> Arguments<'a> {
360 Arguments { pieces, fmt: Some(fmt), args }
361 }
362
363 /// Estimates the length of the formatted text.
364 ///
365 /// This is intended to be used for setting initial `String` capacity
366 /// when using `format!`. Note: this is neither the lower nor upper bound.
367 #[inline]
368 pub fn estimated_capacity(&self) -> usize {
369 let pieces_length: usize = self.pieces.iter().map(|x| x.len()).sum();
370
371 if self.args.is_empty() {
372 pieces_length
373 } else if !self.pieces.is_empty() && self.pieces[0].is_empty() && pieces_length < 16 {
374 // If the format string starts with an argument,
375 // don't preallocate anything, unless length
376 // of pieces is significant.
377 0
378 } else {
379 // There are some arguments, so any additional push
380 // will reallocate the string. To avoid that,
381 // we're "pre-doubling" the capacity here.
382 pieces_length.checked_mul(2).unwrap_or(0)
383 }
384 }
385}
386
387impl<'a> Arguments<'a> {
388 /// Get the formatted string, if it has no arguments to be formatted at runtime.
389 ///
390 /// This can be used to avoid allocations in some cases.
391 ///
392 /// # Guarantees
393 ///
394 /// For `format_args!("just a literal")`, this function is guaranteed to
395 /// return `Some("just a literal")`.
396 ///
397 /// For most cases with placeholders, this function will return `None`.
398 ///
399 /// However, the compiler may perform optimizations that can cause this
400 /// function to return `Some(_)` even if the format string contains
401 /// placeholders. For example, `format_args!("Hello, {}!", "world")` may be
402 /// optimized to `format_args!("Hello, world!")`, such that `as_str()`
403 /// returns `Some("Hello, world!")`.
404 ///
405 /// The behavior for anything but the trivial case (without placeholders)
406 /// is not guaranteed, and should not be relied upon for anything other
407 /// than optimization.
408 ///
409 /// # Examples
410 ///
411 /// ```rust
412 /// use std::fmt::Arguments;
413 ///
414 /// fn write_str(_: &str) { /* ... */ }
415 ///
416 /// fn write_fmt(args: &Arguments<'_>) {
417 /// if let Some(s) = args.as_str() {
418 /// write_str(s)
419 /// } else {
420 /// write_str(&args.to_string());
421 /// }
422 /// }
423 /// ```
424 ///
425 /// ```rust
426 /// assert_eq!(format_args!("hello").as_str(), Some("hello"));
427 /// assert_eq!(format_args!("").as_str(), Some(""));
428 /// assert_eq!(format_args!("{:?}", std::env::current_dir()).as_str(), None);
429 /// ```
430 #[stable(feature = "fmt_as_str", since = "1.52.0")]
431 #[rustc_const_unstable(feature = "const_arguments_as_str", issue = "103900")]
432 #[must_use]
433 #[inline]
434 pub const fn as_str(&self) -> Option<&'static str> {
435 match (self.pieces, self.args) {
436 ([], []) => Some(""),
437 ([s], []) => Some(s),
438 _ => None,
439 }
440 }
441
442 /// Same as [`Arguments::as_str`], but will only return `Some(s)` if it can be determined at compile time.
443 #[must_use]
444 #[inline]
445 fn as_statically_known_str(&self) -> Option<&'static str> {
446 let s = self.as_str();
447 if core::intrinsics::is_val_statically_known(s.is_some()) { s } else { None }
448 }
449}
450
451#[stable(feature = "rust1", since = "1.0.0")]
452impl Debug for Arguments<'_> {
453 fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
454 Display::fmt(self, f:fmt)
455 }
456}
457
458#[stable(feature = "rust1", since = "1.0.0")]
459impl Display for Arguments<'_> {
460 fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
461 write(output:fmt.buf, *self)
462 }
463}
464
465/// `?` formatting.
466///
467/// `Debug` should format the output in a programmer-facing, debugging context.
468///
469/// Generally speaking, you should just `derive` a `Debug` implementation.
470///
471/// When used with the alternate format specifier `#?`, the output is pretty-printed.
472///
473/// For more information on formatters, see [the module-level documentation][module].
474///
475/// [module]: ../../std/fmt/index.html
476///
477/// This trait can be used with `#[derive]` if all fields implement `Debug`. When
478/// `derive`d for structs, it will use the name of the `struct`, then `{`, then a
479/// comma-separated list of each field's name and `Debug` value, then `}`. For
480/// `enum`s, it will use the name of the variant and, if applicable, `(`, then the
481/// `Debug` values of the fields, then `)`.
482///
483/// # Stability
484///
485/// Derived `Debug` formats are not stable, and so may change with future Rust
486/// versions. Additionally, `Debug` implementations of types provided by the
487/// standard library (`std`, `core`, `alloc`, etc.) are not stable, and
488/// may also change with future Rust versions.
489///
490/// # Examples
491///
492/// Deriving an implementation:
493///
494/// ```
495/// #[derive(Debug)]
496/// struct Point {
497/// x: i32,
498/// y: i32,
499/// }
500///
501/// let origin = Point { x: 0, y: 0 };
502///
503/// assert_eq!(format!("The origin is: {origin:?}"), "The origin is: Point { x: 0, y: 0 }");
504/// ```
505///
506/// Manually implementing:
507///
508/// ```
509/// use std::fmt;
510///
511/// struct Point {
512/// x: i32,
513/// y: i32,
514/// }
515///
516/// impl fmt::Debug for Point {
517/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
518/// f.debug_struct("Point")
519/// .field("x", &self.x)
520/// .field("y", &self.y)
521/// .finish()
522/// }
523/// }
524///
525/// let origin = Point { x: 0, y: 0 };
526///
527/// assert_eq!(format!("The origin is: {origin:?}"), "The origin is: Point { x: 0, y: 0 }");
528/// ```
529///
530/// There are a number of helper methods on the [`Formatter`] struct to help you with manual
531/// implementations, such as [`debug_struct`].
532///
533/// [`debug_struct`]: Formatter::debug_struct
534///
535/// Types that do not wish to use the standard suite of debug representations
536/// provided by the `Formatter` trait (`debug_struct`, `debug_tuple`,
537/// `debug_list`, `debug_set`, `debug_map`) can do something totally custom by
538/// manually writing an arbitrary representation to the `Formatter`.
539///
540/// ```
541/// # use std::fmt;
542/// # struct Point {
543/// # x: i32,
544/// # y: i32,
545/// # }
546/// #
547/// impl fmt::Debug for Point {
548/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
549/// write!(f, "Point [{} {}]", self.x, self.y)
550/// }
551/// }
552/// ```
553///
554/// `Debug` implementations using either `derive` or the debug builder API
555/// on [`Formatter`] support pretty-printing using the alternate flag: `{:#?}`.
556///
557/// Pretty-printing with `#?`:
558///
559/// ```
560/// #[derive(Debug)]
561/// struct Point {
562/// x: i32,
563/// y: i32,
564/// }
565///
566/// let origin = Point { x: 0, y: 0 };
567///
568/// assert_eq!(format!("The origin is: {origin:#?}"),
569/// "The origin is: Point {
570/// x: 0,
571/// y: 0,
572/// }");
573/// ```
574
575#[stable(feature = "rust1", since = "1.0.0")]
576#[rustc_on_unimplemented(
577 on(
578 crate_local,
579 label = "`{Self}` cannot be formatted using `{{:?}}`",
580 note = "add `#[derive(Debug)]` to `{Self}` or manually `impl {Debug} for {Self}`"
581 ),
582 message = "`{Self}` doesn't implement `{Debug}`",
583 label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{Debug}`"
584)]
585#[doc(alias = "{:?}")]
586#[rustc_diagnostic_item = "Debug"]
587#[rustc_trivial_field_reads]
588pub trait Debug {
589 /// Formats the value using the given formatter.
590 ///
591 /// # Examples
592 ///
593 /// ```
594 /// use std::fmt;
595 ///
596 /// struct Position {
597 /// longitude: f32,
598 /// latitude: f32,
599 /// }
600 ///
601 /// impl fmt::Debug for Position {
602 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
603 /// f.debug_tuple("")
604 /// .field(&self.longitude)
605 /// .field(&self.latitude)
606 /// .finish()
607 /// }
608 /// }
609 ///
610 /// let position = Position { longitude: 1.987, latitude: 2.983 };
611 /// assert_eq!(format!("{position:?}"), "(1.987, 2.983)");
612 ///
613 /// assert_eq!(format!("{position:#?}"), "(
614 /// 1.987,
615 /// 2.983,
616 /// )");
617 /// ```
618 #[stable(feature = "rust1", since = "1.0.0")]
619 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
620}
621
622// Separate module to reexport the macro `Debug` from prelude without the trait `Debug`.
623pub(crate) mod macros {
624 /// Derive macro generating an impl of the trait `Debug`.
625 #[rustc_builtin_macro]
626 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
627 #[allow_internal_unstable(core_intrinsics, fmt_helpers_for_derive)]
628 pub macro Debug($item:item) {
629 /* compiler built-in */
630 }
631}
632#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
633#[doc(inline)]
634pub use macros::Debug;
635
636/// Format trait for an empty format, `{}`.
637///
638/// Implementing this trait for a type will automatically implement the
639/// [`ToString`][tostring] trait for the type, allowing the usage
640/// of the [`.to_string()`][tostring_function] method. Prefer implementing
641/// the `Display` trait for a type, rather than [`ToString`][tostring].
642///
643/// `Display` is similar to [`Debug`], but `Display` is for user-facing
644/// output, and so cannot be derived.
645///
646/// For more information on formatters, see [the module-level documentation][module].
647///
648/// [module]: ../../std/fmt/index.html
649/// [tostring]: ../../std/string/trait.ToString.html
650/// [tostring_function]: ../../std/string/trait.ToString.html#tymethod.to_string
651///
652/// # Internationalization
653///
654/// Because a type can only have one `Display` implementation, it is often preferable
655/// to only implement `Display` when there is a single most "obvious" way that
656/// values can be formatted as text. This could mean formatting according to the
657/// "invariant" culture and "undefined" locale, or it could mean that the type
658/// display is designed for a specific culture/locale, such as developer logs.
659///
660/// If not all values have a justifiably canonical textual format or if you want
661/// to support alternative formats not covered by the standard set of possible
662/// [formatting traits], the most flexible approach is display adapters: methods
663/// like [`str::escape_default`] or [`Path::display`] which create a wrapper
664/// implementing `Display` to output the specific display format.
665///
666/// [formatting traits]: ../../std/fmt/index.html#formatting-traits
667/// [`Path::display`]: ../../std/path/struct.Path.html#method.display
668///
669/// # Examples
670///
671/// Implementing `Display` on a type:
672///
673/// ```
674/// use std::fmt;
675///
676/// struct Point {
677/// x: i32,
678/// y: i32,
679/// }
680///
681/// impl fmt::Display for Point {
682/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
683/// write!(f, "({}, {})", self.x, self.y)
684/// }
685/// }
686///
687/// let origin = Point { x: 0, y: 0 };
688///
689/// assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");
690/// ```
691#[rustc_on_unimplemented(
692 on(
693 any(_Self = "std::path::Path", _Self = "std::path::PathBuf"),
694 label = "`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
695 note = "call `.display()` or `.to_string_lossy()` to safely print paths, \
696 as they may contain non-Unicode data"
697 ),
698 message = "`{Self}` doesn't implement `{Display}`",
699 label = "`{Self}` cannot be formatted with the default formatter",
700 note = "in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead"
701)]
702#[doc(alias = "{}")]
703#[rustc_diagnostic_item = "Display"]
704#[stable(feature = "rust1", since = "1.0.0")]
705pub trait Display {
706 /// Formats the value using the given formatter.
707 ///
708 /// # Examples
709 ///
710 /// ```
711 /// use std::fmt;
712 ///
713 /// struct Position {
714 /// longitude: f32,
715 /// latitude: f32,
716 /// }
717 ///
718 /// impl fmt::Display for Position {
719 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
720 /// write!(f, "({}, {})", self.longitude, self.latitude)
721 /// }
722 /// }
723 ///
724 /// assert_eq!("(1.987, 2.983)",
725 /// format!("{}", Position { longitude: 1.987, latitude: 2.983, }));
726 /// ```
727 #[stable(feature = "rust1", since = "1.0.0")]
728 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
729}
730
731/// `o` formatting.
732///
733/// The `Octal` trait should format its output as a number in base-8.
734///
735/// For primitive signed integers (`i8` to `i128`, and `isize`),
736/// negative values are formatted as the two’s complement representation.
737///
738/// The alternate flag, `#`, adds a `0o` in front of the output.
739///
740/// For more information on formatters, see [the module-level documentation][module].
741///
742/// [module]: ../../std/fmt/index.html
743///
744/// # Examples
745///
746/// Basic usage with `i32`:
747///
748/// ```
749/// let x = 42; // 42 is '52' in octal
750///
751/// assert_eq!(format!("{x:o}"), "52");
752/// assert_eq!(format!("{x:#o}"), "0o52");
753///
754/// assert_eq!(format!("{:o}", -16), "37777777760");
755/// ```
756///
757/// Implementing `Octal` on a type:
758///
759/// ```
760/// use std::fmt;
761///
762/// struct Length(i32);
763///
764/// impl fmt::Octal for Length {
765/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
766/// let val = self.0;
767///
768/// fmt::Octal::fmt(&val, f) // delegate to i32's implementation
769/// }
770/// }
771///
772/// let l = Length(9);
773///
774/// assert_eq!(format!("l as octal is: {l:o}"), "l as octal is: 11");
775///
776/// assert_eq!(format!("l as octal is: {l:#06o}"), "l as octal is: 0o0011");
777/// ```
778#[stable(feature = "rust1", since = "1.0.0")]
779pub trait Octal {
780 /// Formats the value using the given formatter.
781 #[stable(feature = "rust1", since = "1.0.0")]
782 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
783}
784
785/// `b` formatting.
786///
787/// The `Binary` trait should format its output as a number in binary.
788///
789/// For primitive signed integers ([`i8`] to [`i128`], and [`isize`]),
790/// negative values are formatted as the two’s complement representation.
791///
792/// The alternate flag, `#`, adds a `0b` in front of the output.
793///
794/// For more information on formatters, see [the module-level documentation][module].
795///
796/// [module]: ../../std/fmt/index.html
797///
798/// # Examples
799///
800/// Basic usage with [`i32`]:
801///
802/// ```
803/// let x = 42; // 42 is '101010' in binary
804///
805/// assert_eq!(format!("{x:b}"), "101010");
806/// assert_eq!(format!("{x:#b}"), "0b101010");
807///
808/// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");
809/// ```
810///
811/// Implementing `Binary` on a type:
812///
813/// ```
814/// use std::fmt;
815///
816/// struct Length(i32);
817///
818/// impl fmt::Binary for Length {
819/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
820/// let val = self.0;
821///
822/// fmt::Binary::fmt(&val, f) // delegate to i32's implementation
823/// }
824/// }
825///
826/// let l = Length(107);
827///
828/// assert_eq!(format!("l as binary is: {l:b}"), "l as binary is: 1101011");
829///
830/// assert_eq!(
831/// // Note that the `0b` prefix added by `#` is included in the total width, so we
832/// // need to add two to correctly display all 32 bits.
833/// format!("l as binary is: {l:#034b}"),
834/// "l as binary is: 0b00000000000000000000000001101011"
835/// );
836/// ```
837#[stable(feature = "rust1", since = "1.0.0")]
838pub trait Binary {
839 /// Formats the value using the given formatter.
840 #[stable(feature = "rust1", since = "1.0.0")]
841 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
842}
843
844/// `x` formatting.
845///
846/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
847/// in lower case.
848///
849/// For primitive signed integers (`i8` to `i128`, and `isize`),
850/// negative values are formatted as the two’s complement representation.
851///
852/// The alternate flag, `#`, adds a `0x` in front of the output.
853///
854/// For more information on formatters, see [the module-level documentation][module].
855///
856/// [module]: ../../std/fmt/index.html
857///
858/// # Examples
859///
860/// Basic usage with `i32`:
861///
862/// ```
863/// let y = 42; // 42 is '2a' in hex
864///
865/// assert_eq!(format!("{y:x}"), "2a");
866/// assert_eq!(format!("{y:#x}"), "0x2a");
867///
868/// assert_eq!(format!("{:x}", -16), "fffffff0");
869/// ```
870///
871/// Implementing `LowerHex` on a type:
872///
873/// ```
874/// use std::fmt;
875///
876/// struct Length(i32);
877///
878/// impl fmt::LowerHex for Length {
879/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
880/// let val = self.0;
881///
882/// fmt::LowerHex::fmt(&val, f) // delegate to i32's implementation
883/// }
884/// }
885///
886/// let l = Length(9);
887///
888/// assert_eq!(format!("l as hex is: {l:x}"), "l as hex is: 9");
889///
890/// assert_eq!(format!("l as hex is: {l:#010x}"), "l as hex is: 0x00000009");
891/// ```
892#[stable(feature = "rust1", since = "1.0.0")]
893pub trait LowerHex {
894 /// Formats the value using the given formatter.
895 #[stable(feature = "rust1", since = "1.0.0")]
896 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
897}
898
899/// `X` formatting.
900///
901/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
902/// in upper case.
903///
904/// For primitive signed integers (`i8` to `i128`, and `isize`),
905/// negative values are formatted as the two’s complement representation.
906///
907/// The alternate flag, `#`, adds a `0x` in front of the output.
908///
909/// For more information on formatters, see [the module-level documentation][module].
910///
911/// [module]: ../../std/fmt/index.html
912///
913/// # Examples
914///
915/// Basic usage with `i32`:
916///
917/// ```
918/// let y = 42; // 42 is '2A' in hex
919///
920/// assert_eq!(format!("{y:X}"), "2A");
921/// assert_eq!(format!("{y:#X}"), "0x2A");
922///
923/// assert_eq!(format!("{:X}", -16), "FFFFFFF0");
924/// ```
925///
926/// Implementing `UpperHex` on a type:
927///
928/// ```
929/// use std::fmt;
930///
931/// struct Length(i32);
932///
933/// impl fmt::UpperHex for Length {
934/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
935/// let val = self.0;
936///
937/// fmt::UpperHex::fmt(&val, f) // delegate to i32's implementation
938/// }
939/// }
940///
941/// let l = Length(i32::MAX);
942///
943/// assert_eq!(format!("l as hex is: {l:X}"), "l as hex is: 7FFFFFFF");
944///
945/// assert_eq!(format!("l as hex is: {l:#010X}"), "l as hex is: 0x7FFFFFFF");
946/// ```
947#[stable(feature = "rust1", since = "1.0.0")]
948pub trait UpperHex {
949 /// Formats the value using the given formatter.
950 #[stable(feature = "rust1", since = "1.0.0")]
951 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
952}
953
954/// `p` formatting.
955///
956/// The `Pointer` trait should format its output as a memory location. This is commonly presented
957/// as hexadecimal.
958///
959/// For more information on formatters, see [the module-level documentation][module].
960///
961/// [module]: ../../std/fmt/index.html
962///
963/// # Examples
964///
965/// Basic usage with `&i32`:
966///
967/// ```
968/// let x = &42;
969///
970/// let address = format!("{x:p}"); // this produces something like '0x7f06092ac6d0'
971/// ```
972///
973/// Implementing `Pointer` on a type:
974///
975/// ```
976/// use std::fmt;
977///
978/// struct Length(i32);
979///
980/// impl fmt::Pointer for Length {
981/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
982/// // use `as` to convert to a `*const T`, which implements Pointer, which we can use
983///
984/// let ptr = self as *const Self;
985/// fmt::Pointer::fmt(&ptr, f)
986/// }
987/// }
988///
989/// let l = Length(42);
990///
991/// println!("l is in memory here: {l:p}");
992///
993/// let l_ptr = format!("{l:018p}");
994/// assert_eq!(l_ptr.len(), 18);
995/// assert_eq!(&l_ptr[..2], "0x");
996/// ```
997#[stable(feature = "rust1", since = "1.0.0")]
998#[rustc_diagnostic_item = "Pointer"]
999pub trait Pointer {
1000 /// Formats the value using the given formatter.
1001 #[stable(feature = "rust1", since = "1.0.0")]
1002 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1003}
1004
1005/// `e` formatting.
1006///
1007/// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
1008///
1009/// For more information on formatters, see [the module-level documentation][module].
1010///
1011/// [module]: ../../std/fmt/index.html
1012///
1013/// # Examples
1014///
1015/// Basic usage with `f64`:
1016///
1017/// ```
1018/// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
1019///
1020/// assert_eq!(format!("{x:e}"), "4.2e1");
1021/// ```
1022///
1023/// Implementing `LowerExp` on a type:
1024///
1025/// ```
1026/// use std::fmt;
1027///
1028/// struct Length(i32);
1029///
1030/// impl fmt::LowerExp for Length {
1031/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1032/// let val = f64::from(self.0);
1033/// fmt::LowerExp::fmt(&val, f) // delegate to f64's implementation
1034/// }
1035/// }
1036///
1037/// let l = Length(100);
1038///
1039/// assert_eq!(
1040/// format!("l in scientific notation is: {l:e}"),
1041/// "l in scientific notation is: 1e2"
1042/// );
1043///
1044/// assert_eq!(
1045/// format!("l in scientific notation is: {l:05e}"),
1046/// "l in scientific notation is: 001e2"
1047/// );
1048/// ```
1049#[stable(feature = "rust1", since = "1.0.0")]
1050pub trait LowerExp {
1051 /// Formats the value using the given formatter.
1052 #[stable(feature = "rust1", since = "1.0.0")]
1053 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1054}
1055
1056/// `E` formatting.
1057///
1058/// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
1059///
1060/// For more information on formatters, see [the module-level documentation][module].
1061///
1062/// [module]: ../../std/fmt/index.html
1063///
1064/// # Examples
1065///
1066/// Basic usage with `f64`:
1067///
1068/// ```
1069/// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
1070///
1071/// assert_eq!(format!("{x:E}"), "4.2E1");
1072/// ```
1073///
1074/// Implementing `UpperExp` on a type:
1075///
1076/// ```
1077/// use std::fmt;
1078///
1079/// struct Length(i32);
1080///
1081/// impl fmt::UpperExp for Length {
1082/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1083/// let val = f64::from(self.0);
1084/// fmt::UpperExp::fmt(&val, f) // delegate to f64's implementation
1085/// }
1086/// }
1087///
1088/// let l = Length(100);
1089///
1090/// assert_eq!(
1091/// format!("l in scientific notation is: {l:E}"),
1092/// "l in scientific notation is: 1E2"
1093/// );
1094///
1095/// assert_eq!(
1096/// format!("l in scientific notation is: {l:05E}"),
1097/// "l in scientific notation is: 001E2"
1098/// );
1099/// ```
1100#[stable(feature = "rust1", since = "1.0.0")]
1101pub trait UpperExp {
1102 /// Formats the value using the given formatter.
1103 #[stable(feature = "rust1", since = "1.0.0")]
1104 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1105}
1106
1107/// The `write` function takes an output stream, and an `Arguments` struct
1108/// that can be precompiled with the `format_args!` macro.
1109///
1110/// The arguments will be formatted according to the specified format string
1111/// into the output stream provided.
1112///
1113/// # Examples
1114///
1115/// Basic usage:
1116///
1117/// ```
1118/// use std::fmt;
1119///
1120/// let mut output = String::new();
1121/// fmt::write(&mut output, format_args!("Hello {}!", "world"))
1122/// .expect("Error occurred while trying to write in String");
1123/// assert_eq!(output, "Hello world!");
1124/// ```
1125///
1126/// Please note that using [`write!`] might be preferable. Example:
1127///
1128/// ```
1129/// use std::fmt::Write;
1130///
1131/// let mut output = String::new();
1132/// write!(&mut output, "Hello {}!", "world")
1133/// .expect("Error occurred while trying to write in String");
1134/// assert_eq!(output, "Hello world!");
1135/// ```
1136///
1137/// [`write!`]: crate::write!
1138#[stable(feature = "rust1", since = "1.0.0")]
1139pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
1140 let mut formatter = Formatter::new(output);
1141 let mut idx = 0;
1142
1143 match args.fmt {
1144 None => {
1145 // We can use default formatting parameters for all arguments.
1146 for (i, arg) in args.args.iter().enumerate() {
1147 // SAFETY: args.args and args.pieces come from the same Arguments,
1148 // which guarantees the indexes are always within bounds.
1149 let piece = unsafe { args.pieces.get_unchecked(i) };
1150 if !piece.is_empty() {
1151 formatter.buf.write_str(*piece)?;
1152 }
1153
1154 // SAFETY: There are no formatting parameters and hence no
1155 // count arguments.
1156 unsafe {
1157 arg.fmt(&mut formatter)?;
1158 }
1159 idx += 1;
1160 }
1161 }
1162 Some(fmt) => {
1163 // Every spec has a corresponding argument that is preceded by
1164 // a string piece.
1165 for (i, arg) in fmt.iter().enumerate() {
1166 // SAFETY: fmt and args.pieces come from the same Arguments,
1167 // which guarantees the indexes are always within bounds.
1168 let piece = unsafe { args.pieces.get_unchecked(i) };
1169 if !piece.is_empty() {
1170 formatter.buf.write_str(*piece)?;
1171 }
1172 // SAFETY: arg and args.args come from the same Arguments,
1173 // which guarantees the indexes are always within bounds.
1174 unsafe { run(&mut formatter, arg, args.args) }?;
1175 idx += 1;
1176 }
1177 }
1178 }
1179
1180 // There can be only one trailing string piece left.
1181 if let Some(piece) = args.pieces.get(idx) {
1182 formatter.buf.write_str(*piece)?;
1183 }
1184
1185 Ok(())
1186}
1187
1188unsafe fn run(fmt: &mut Formatter<'_>, arg: &rt::Placeholder, args: &[rt::Argument<'_>]) -> Result {
1189 fmt.fill = arg.fill;
1190 fmt.align = arg.align;
1191 fmt.flags = arg.flags;
1192 // SAFETY: arg and args come from the same Arguments,
1193 // which guarantees the indexes are always within bounds.
1194 unsafe {
1195 fmt.width = getcount(args, &arg.width);
1196 fmt.precision = getcount(args, &arg.precision);
1197 }
1198
1199 // Extract the correct argument
1200 debug_assert!(arg.position < args.len());
1201 // SAFETY: arg and args come from the same Arguments,
1202 // which guarantees its index is always within bounds.
1203 let value: &Argument<'_> = unsafe { args.get_unchecked(index:arg.position) };
1204
1205 // Then actually do some printing
1206 // SAFETY: this is a placeholder argument.
1207 unsafe { value.fmt(fmt) }
1208}
1209
1210unsafe fn getcount(args: &[rt::Argument<'_>], cnt: &rt::Count) -> Option<usize> {
1211 match *cnt {
1212 rt::Count::Is(n: usize) => Some(n),
1213 rt::Count::Implied => None,
1214 rt::Count::Param(i: usize) => {
1215 debug_assert!(i < args.len());
1216 // SAFETY: cnt and args come from the same Arguments,
1217 // which guarantees this index is always within bounds.
1218 unsafe { args.get_unchecked(index:i).as_usize() }
1219 }
1220 }
1221}
1222
1223/// Padding after the end of something. Returned by `Formatter::padding`.
1224#[must_use = "don't forget to write the post padding"]
1225pub(crate) struct PostPadding {
1226 fill: char,
1227 padding: usize,
1228}
1229
1230impl PostPadding {
1231 fn new(fill: char, padding: usize) -> PostPadding {
1232 PostPadding { fill, padding }
1233 }
1234
1235 /// Write this post padding.
1236 pub(crate) fn write(self, f: &mut Formatter<'_>) -> Result {
1237 for _ in 0..self.padding {
1238 f.buf.write_char(self.fill)?;
1239 }
1240 Ok(())
1241 }
1242}
1243
1244impl<'a> Formatter<'a> {
1245 fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c>
1246 where
1247 'b: 'c,
1248 F: FnOnce(&'b mut (dyn Write + 'b)) -> &'c mut (dyn Write + 'c),
1249 {
1250 Formatter {
1251 // We want to change this
1252 buf: wrap(self.buf),
1253
1254 // And preserve these
1255 flags: self.flags,
1256 fill: self.fill,
1257 align: self.align,
1258 width: self.width,
1259 precision: self.precision,
1260 }
1261 }
1262
1263 // Helper methods used for padding and processing formatting arguments that
1264 // all formatting traits can use.
1265
1266 /// Performs the correct padding for an integer which has already been
1267 /// emitted into a str. The str should *not* contain the sign for the
1268 /// integer, that will be added by this method.
1269 ///
1270 /// # Arguments
1271 ///
1272 /// * is_nonnegative - whether the original integer was either positive or zero.
1273 /// * prefix - if the '#' character (Alternate) is provided, this
1274 /// is the prefix to put in front of the number.
1275 /// * buf - the byte array that the number has been formatted into
1276 ///
1277 /// This function will correctly account for the flags provided as well as
1278 /// the minimum width. It will not take precision into account.
1279 ///
1280 /// # Examples
1281 ///
1282 /// ```
1283 /// use std::fmt;
1284 ///
1285 /// struct Foo { nb: i32 }
1286 ///
1287 /// impl Foo {
1288 /// fn new(nb: i32) -> Foo {
1289 /// Foo {
1290 /// nb,
1291 /// }
1292 /// }
1293 /// }
1294 ///
1295 /// impl fmt::Display for Foo {
1296 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1297 /// // We need to remove "-" from the number output.
1298 /// let tmp = self.nb.abs().to_string();
1299 ///
1300 /// formatter.pad_integral(self.nb >= 0, "Foo ", &tmp)
1301 /// }
1302 /// }
1303 ///
1304 /// assert_eq!(format!("{}", Foo::new(2)), "2");
1305 /// assert_eq!(format!("{}", Foo::new(-1)), "-1");
1306 /// assert_eq!(format!("{}", Foo::new(0)), "0");
1307 /// assert_eq!(format!("{:#}", Foo::new(-1)), "-Foo 1");
1308 /// assert_eq!(format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
1309 /// ```
1310 #[stable(feature = "rust1", since = "1.0.0")]
1311 pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result {
1312 let mut width = buf.len();
1313
1314 let mut sign = None;
1315 if !is_nonnegative {
1316 sign = Some('-');
1317 width += 1;
1318 } else if self.sign_plus() {
1319 sign = Some('+');
1320 width += 1;
1321 }
1322
1323 let prefix = if self.alternate() {
1324 width += prefix.chars().count();
1325 Some(prefix)
1326 } else {
1327 None
1328 };
1329
1330 // Writes the sign if it exists, and then the prefix if it was requested
1331 #[inline(never)]
1332 fn write_prefix(f: &mut Formatter<'_>, sign: Option<char>, prefix: Option<&str>) -> Result {
1333 if let Some(c) = sign {
1334 f.buf.write_char(c)?;
1335 }
1336 if let Some(prefix) = prefix { f.buf.write_str(prefix) } else { Ok(()) }
1337 }
1338
1339 // The `width` field is more of a `min-width` parameter at this point.
1340 match self.width {
1341 // If there's no minimum length requirements then we can just
1342 // write the bytes.
1343 None => {
1344 write_prefix(self, sign, prefix)?;
1345 self.buf.write_str(buf)
1346 }
1347 // Check if we're over the minimum width, if so then we can also
1348 // just write the bytes.
1349 Some(min) if width >= min => {
1350 write_prefix(self, sign, prefix)?;
1351 self.buf.write_str(buf)
1352 }
1353 // The sign and prefix goes before the padding if the fill character
1354 // is zero
1355 Some(min) if self.sign_aware_zero_pad() => {
1356 let old_fill = crate::mem::replace(&mut self.fill, '0');
1357 let old_align = crate::mem::replace(&mut self.align, rt::Alignment::Right);
1358 write_prefix(self, sign, prefix)?;
1359 let post_padding = self.padding(min - width, Alignment::Right)?;
1360 self.buf.write_str(buf)?;
1361 post_padding.write(self)?;
1362 self.fill = old_fill;
1363 self.align = old_align;
1364 Ok(())
1365 }
1366 // Otherwise, the sign and prefix goes after the padding
1367 Some(min) => {
1368 let post_padding = self.padding(min - width, Alignment::Right)?;
1369 write_prefix(self, sign, prefix)?;
1370 self.buf.write_str(buf)?;
1371 post_padding.write(self)
1372 }
1373 }
1374 }
1375
1376 /// This function takes a string slice and emits it to the internal buffer
1377 /// after applying the relevant formatting flags specified. The flags
1378 /// recognized for generic strings are:
1379 ///
1380 /// * width - the minimum width of what to emit
1381 /// * fill/align - what to emit and where to emit it if the string
1382 /// provided needs to be padded
1383 /// * precision - the maximum length to emit, the string is truncated if it
1384 /// is longer than this length
1385 ///
1386 /// Notably this function ignores the `flag` parameters.
1387 ///
1388 /// # Examples
1389 ///
1390 /// ```
1391 /// use std::fmt;
1392 ///
1393 /// struct Foo;
1394 ///
1395 /// impl fmt::Display for Foo {
1396 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1397 /// formatter.pad("Foo")
1398 /// }
1399 /// }
1400 ///
1401 /// assert_eq!(format!("{Foo:<4}"), "Foo ");
1402 /// assert_eq!(format!("{Foo:0>4}"), "0Foo");
1403 /// ```
1404 #[stable(feature = "rust1", since = "1.0.0")]
1405 pub fn pad(&mut self, s: &str) -> Result {
1406 // Make sure there's a fast path up front
1407 if self.width.is_none() && self.precision.is_none() {
1408 return self.buf.write_str(s);
1409 }
1410 // The `precision` field can be interpreted as a `max-width` for the
1411 // string being formatted.
1412 let s = if let Some(max) = self.precision {
1413 // If our string is longer that the precision, then we must have
1414 // truncation. However other flags like `fill`, `width` and `align`
1415 // must act as always.
1416 if let Some((i, _)) = s.char_indices().nth(max) {
1417 // LLVM here can't prove that `..i` won't panic `&s[..i]`, but
1418 // we know that it can't panic. Use `get` + `unwrap_or` to avoid
1419 // `unsafe` and otherwise don't emit any panic-related code
1420 // here.
1421 s.get(..i).unwrap_or(s)
1422 } else {
1423 &s
1424 }
1425 } else {
1426 &s
1427 };
1428 // The `width` field is more of a `min-width` parameter at this point.
1429 match self.width {
1430 // If we're under the maximum length, and there's no minimum length
1431 // requirements, then we can just emit the string
1432 None => self.buf.write_str(s),
1433 Some(width) => {
1434 let chars_count = s.chars().count();
1435 // If we're under the maximum width, check if we're over the minimum
1436 // width, if so it's as easy as just emitting the string.
1437 if chars_count >= width {
1438 self.buf.write_str(s)
1439 }
1440 // If we're under both the maximum and the minimum width, then fill
1441 // up the minimum width with the specified string + some alignment.
1442 else {
1443 let align = Alignment::Left;
1444 let post_padding = self.padding(width - chars_count, align)?;
1445 self.buf.write_str(s)?;
1446 post_padding.write(self)
1447 }
1448 }
1449 }
1450 }
1451
1452 /// Write the pre-padding and return the unwritten post-padding. Callers are
1453 /// responsible for ensuring post-padding is written after the thing that is
1454 /// being padded.
1455 pub(crate) fn padding(
1456 &mut self,
1457 padding: usize,
1458 default: Alignment,
1459 ) -> result::Result<PostPadding, Error> {
1460 let align = match self.align {
1461 rt::Alignment::Unknown => default,
1462 rt::Alignment::Left => Alignment::Left,
1463 rt::Alignment::Right => Alignment::Right,
1464 rt::Alignment::Center => Alignment::Center,
1465 };
1466
1467 let (pre_pad, post_pad) = match align {
1468 Alignment::Left => (0, padding),
1469 Alignment::Right => (padding, 0),
1470 Alignment::Center => (padding / 2, (padding + 1) / 2),
1471 };
1472
1473 for _ in 0..pre_pad {
1474 self.buf.write_char(self.fill)?;
1475 }
1476
1477 Ok(PostPadding::new(self.fill, post_pad))
1478 }
1479
1480 /// Takes the formatted parts and applies the padding.
1481 /// Assumes that the caller already has rendered the parts with required precision,
1482 /// so that `self.precision` can be ignored.
1483 ///
1484 /// # Safety
1485 ///
1486 /// Any `numfmt::Part::Copy` parts in `formatted` must contain valid UTF-8.
1487 unsafe fn pad_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
1488 if let Some(mut width) = self.width {
1489 // for the sign-aware zero padding, we render the sign first and
1490 // behave as if we had no sign from the beginning.
1491 let mut formatted = formatted.clone();
1492 let old_fill = self.fill;
1493 let old_align = self.align;
1494 if self.sign_aware_zero_pad() {
1495 // a sign always goes first
1496 let sign = formatted.sign;
1497 self.buf.write_str(sign)?;
1498
1499 // remove the sign from the formatted parts
1500 formatted.sign = "";
1501 width = width.saturating_sub(sign.len());
1502 self.fill = '0';
1503 self.align = rt::Alignment::Right;
1504 }
1505
1506 // remaining parts go through the ordinary padding process.
1507 let len = formatted.len();
1508 let ret = if width <= len {
1509 // no padding
1510 // SAFETY: Per the precondition.
1511 unsafe { self.write_formatted_parts(&formatted) }
1512 } else {
1513 let post_padding = self.padding(width - len, Alignment::Right)?;
1514 // SAFETY: Per the precondition.
1515 unsafe {
1516 self.write_formatted_parts(&formatted)?;
1517 }
1518 post_padding.write(self)
1519 };
1520 self.fill = old_fill;
1521 self.align = old_align;
1522 ret
1523 } else {
1524 // this is the common case and we take a shortcut
1525 // SAFETY: Per the precondition.
1526 unsafe { self.write_formatted_parts(formatted) }
1527 }
1528 }
1529
1530 /// # Safety
1531 ///
1532 /// Any `numfmt::Part::Copy` parts in `formatted` must contain valid UTF-8.
1533 unsafe fn write_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
1534 unsafe fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result {
1535 // SAFETY: This is used for `numfmt::Part::Num` and `numfmt::Part::Copy`.
1536 // It's safe to use for `numfmt::Part::Num` since every char `c` is between
1537 // `b'0'` and `b'9'`, which means `s` is valid UTF-8. It's safe to use for
1538 // `numfmt::Part::Copy` due to this function's precondition.
1539 buf.write_str(unsafe { str::from_utf8_unchecked(s) })
1540 }
1541
1542 if !formatted.sign.is_empty() {
1543 self.buf.write_str(formatted.sign)?;
1544 }
1545 for part in formatted.parts {
1546 match *part {
1547 numfmt::Part::Zero(mut nzeroes) => {
1548 const ZEROES: &str = // 64 zeroes
1549 "0000000000000000000000000000000000000000000000000000000000000000";
1550 while nzeroes > ZEROES.len() {
1551 self.buf.write_str(ZEROES)?;
1552 nzeroes -= ZEROES.len();
1553 }
1554 if nzeroes > 0 {
1555 self.buf.write_str(&ZEROES[..nzeroes])?;
1556 }
1557 }
1558 numfmt::Part::Num(mut v) => {
1559 let mut s = [0; 5];
1560 let len = part.len();
1561 for c in s[..len].iter_mut().rev() {
1562 *c = b'0' + (v % 10) as u8;
1563 v /= 10;
1564 }
1565 // SAFETY: Per the precondition.
1566 unsafe {
1567 write_bytes(self.buf, &s[..len])?;
1568 }
1569 }
1570 // SAFETY: Per the precondition.
1571 numfmt::Part::Copy(buf) => unsafe {
1572 write_bytes(self.buf, buf)?;
1573 },
1574 }
1575 }
1576 Ok(())
1577 }
1578
1579 /// Writes some data to the underlying buffer contained within this
1580 /// formatter.
1581 ///
1582 /// # Examples
1583 ///
1584 /// ```
1585 /// use std::fmt;
1586 ///
1587 /// struct Foo;
1588 ///
1589 /// impl fmt::Display for Foo {
1590 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1591 /// formatter.write_str("Foo")
1592 /// // This is equivalent to:
1593 /// // write!(formatter, "Foo")
1594 /// }
1595 /// }
1596 ///
1597 /// assert_eq!(format!("{Foo}"), "Foo");
1598 /// assert_eq!(format!("{Foo:0>8}"), "Foo");
1599 /// ```
1600 #[stable(feature = "rust1", since = "1.0.0")]
1601 pub fn write_str(&mut self, data: &str) -> Result {
1602 self.buf.write_str(data)
1603 }
1604
1605 /// Writes some formatted information into this instance.
1606 ///
1607 /// # Examples
1608 ///
1609 /// ```
1610 /// use std::fmt;
1611 ///
1612 /// struct Foo(i32);
1613 ///
1614 /// impl fmt::Display for Foo {
1615 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1616 /// formatter.write_fmt(format_args!("Foo {}", self.0))
1617 /// }
1618 /// }
1619 ///
1620 /// assert_eq!(format!("{}", Foo(-1)), "Foo -1");
1621 /// assert_eq!(format!("{:0>8}", Foo(2)), "Foo 2");
1622 /// ```
1623 #[stable(feature = "rust1", since = "1.0.0")]
1624 #[inline]
1625 pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
1626 if let Some(s) = fmt.as_statically_known_str() {
1627 self.buf.write_str(s)
1628 } else {
1629 write(self.buf, fmt)
1630 }
1631 }
1632
1633 /// Flags for formatting
1634 #[must_use]
1635 #[stable(feature = "rust1", since = "1.0.0")]
1636 #[deprecated(
1637 since = "1.24.0",
1638 note = "use the `sign_plus`, `sign_minus`, `alternate`, \
1639 or `sign_aware_zero_pad` methods instead"
1640 )]
1641 pub fn flags(&self) -> u32 {
1642 self.flags
1643 }
1644
1645 /// Character used as 'fill' whenever there is alignment.
1646 ///
1647 /// # Examples
1648 ///
1649 /// ```
1650 /// use std::fmt;
1651 ///
1652 /// struct Foo;
1653 ///
1654 /// impl fmt::Display for Foo {
1655 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1656 /// let c = formatter.fill();
1657 /// if let Some(width) = formatter.width() {
1658 /// for _ in 0..width {
1659 /// write!(formatter, "{c}")?;
1660 /// }
1661 /// Ok(())
1662 /// } else {
1663 /// write!(formatter, "{c}")
1664 /// }
1665 /// }
1666 /// }
1667 ///
1668 /// // We set alignment to the right with ">".
1669 /// assert_eq!(format!("{Foo:G>3}"), "GGG");
1670 /// assert_eq!(format!("{Foo:t>6}"), "tttttt");
1671 /// ```
1672 #[must_use]
1673 #[stable(feature = "fmt_flags", since = "1.5.0")]
1674 pub fn fill(&self) -> char {
1675 self.fill
1676 }
1677
1678 /// Flag indicating what form of alignment was requested.
1679 ///
1680 /// # Examples
1681 ///
1682 /// ```
1683 /// use std::fmt::{self, Alignment};
1684 ///
1685 /// struct Foo;
1686 ///
1687 /// impl fmt::Display for Foo {
1688 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1689 /// let s = if let Some(s) = formatter.align() {
1690 /// match s {
1691 /// Alignment::Left => "left",
1692 /// Alignment::Right => "right",
1693 /// Alignment::Center => "center",
1694 /// }
1695 /// } else {
1696 /// "into the void"
1697 /// };
1698 /// write!(formatter, "{s}")
1699 /// }
1700 /// }
1701 ///
1702 /// assert_eq!(format!("{Foo:<}"), "left");
1703 /// assert_eq!(format!("{Foo:>}"), "right");
1704 /// assert_eq!(format!("{Foo:^}"), "center");
1705 /// assert_eq!(format!("{Foo}"), "into the void");
1706 /// ```
1707 #[must_use]
1708 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
1709 pub fn align(&self) -> Option<Alignment> {
1710 match self.align {
1711 rt::Alignment::Left => Some(Alignment::Left),
1712 rt::Alignment::Right => Some(Alignment::Right),
1713 rt::Alignment::Center => Some(Alignment::Center),
1714 rt::Alignment::Unknown => None,
1715 }
1716 }
1717
1718 /// Optionally specified integer width that the output should be.
1719 ///
1720 /// # Examples
1721 ///
1722 /// ```
1723 /// use std::fmt;
1724 ///
1725 /// struct Foo(i32);
1726 ///
1727 /// impl fmt::Display for Foo {
1728 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1729 /// if let Some(width) = formatter.width() {
1730 /// // If we received a width, we use it
1731 /// write!(formatter, "{:width$}", format!("Foo({})", self.0), width = width)
1732 /// } else {
1733 /// // Otherwise we do nothing special
1734 /// write!(formatter, "Foo({})", self.0)
1735 /// }
1736 /// }
1737 /// }
1738 ///
1739 /// assert_eq!(format!("{:10}", Foo(23)), "Foo(23) ");
1740 /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
1741 /// ```
1742 #[must_use]
1743 #[stable(feature = "fmt_flags", since = "1.5.0")]
1744 pub fn width(&self) -> Option<usize> {
1745 self.width
1746 }
1747
1748 /// Optionally specified precision for numeric types. Alternatively, the
1749 /// maximum width for string types.
1750 ///
1751 /// # Examples
1752 ///
1753 /// ```
1754 /// use std::fmt;
1755 ///
1756 /// struct Foo(f32);
1757 ///
1758 /// impl fmt::Display for Foo {
1759 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1760 /// if let Some(precision) = formatter.precision() {
1761 /// // If we received a precision, we use it.
1762 /// write!(formatter, "Foo({1:.*})", precision, self.0)
1763 /// } else {
1764 /// // Otherwise we default to 2.
1765 /// write!(formatter, "Foo({:.2})", self.0)
1766 /// }
1767 /// }
1768 /// }
1769 ///
1770 /// assert_eq!(format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
1771 /// assert_eq!(format!("{}", Foo(23.2)), "Foo(23.20)");
1772 /// ```
1773 #[must_use]
1774 #[stable(feature = "fmt_flags", since = "1.5.0")]
1775 pub fn precision(&self) -> Option<usize> {
1776 self.precision
1777 }
1778
1779 /// Determines if the `+` flag was specified.
1780 ///
1781 /// # Examples
1782 ///
1783 /// ```
1784 /// use std::fmt;
1785 ///
1786 /// struct Foo(i32);
1787 ///
1788 /// impl fmt::Display for Foo {
1789 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1790 /// if formatter.sign_plus() {
1791 /// write!(formatter,
1792 /// "Foo({}{})",
1793 /// if self.0 < 0 { '-' } else { '+' },
1794 /// self.0.abs())
1795 /// } else {
1796 /// write!(formatter, "Foo({})", self.0)
1797 /// }
1798 /// }
1799 /// }
1800 ///
1801 /// assert_eq!(format!("{:+}", Foo(23)), "Foo(+23)");
1802 /// assert_eq!(format!("{:+}", Foo(-23)), "Foo(-23)");
1803 /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
1804 /// ```
1805 #[must_use]
1806 #[stable(feature = "fmt_flags", since = "1.5.0")]
1807 pub fn sign_plus(&self) -> bool {
1808 self.flags & (1 << rt::Flag::SignPlus as u32) != 0
1809 }
1810
1811 /// Determines if the `-` flag was specified.
1812 ///
1813 /// # Examples
1814 ///
1815 /// ```
1816 /// use std::fmt;
1817 ///
1818 /// struct Foo(i32);
1819 ///
1820 /// impl fmt::Display for Foo {
1821 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1822 /// if formatter.sign_minus() {
1823 /// // You want a minus sign? Have one!
1824 /// write!(formatter, "-Foo({})", self.0)
1825 /// } else {
1826 /// write!(formatter, "Foo({})", self.0)
1827 /// }
1828 /// }
1829 /// }
1830 ///
1831 /// assert_eq!(format!("{:-}", Foo(23)), "-Foo(23)");
1832 /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
1833 /// ```
1834 #[must_use]
1835 #[stable(feature = "fmt_flags", since = "1.5.0")]
1836 pub fn sign_minus(&self) -> bool {
1837 self.flags & (1 << rt::Flag::SignMinus as u32) != 0
1838 }
1839
1840 /// Determines if the `#` flag was specified.
1841 ///
1842 /// # Examples
1843 ///
1844 /// ```
1845 /// use std::fmt;
1846 ///
1847 /// struct Foo(i32);
1848 ///
1849 /// impl fmt::Display for Foo {
1850 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1851 /// if formatter.alternate() {
1852 /// write!(formatter, "Foo({})", self.0)
1853 /// } else {
1854 /// write!(formatter, "{}", self.0)
1855 /// }
1856 /// }
1857 /// }
1858 ///
1859 /// assert_eq!(format!("{:#}", Foo(23)), "Foo(23)");
1860 /// assert_eq!(format!("{}", Foo(23)), "23");
1861 /// ```
1862 #[must_use]
1863 #[stable(feature = "fmt_flags", since = "1.5.0")]
1864 pub fn alternate(&self) -> bool {
1865 self.flags & (1 << rt::Flag::Alternate as u32) != 0
1866 }
1867
1868 /// Determines if the `0` flag was specified.
1869 ///
1870 /// # Examples
1871 ///
1872 /// ```
1873 /// use std::fmt;
1874 ///
1875 /// struct Foo(i32);
1876 ///
1877 /// impl fmt::Display for Foo {
1878 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1879 /// assert!(formatter.sign_aware_zero_pad());
1880 /// assert_eq!(formatter.width(), Some(4));
1881 /// // We ignore the formatter's options.
1882 /// write!(formatter, "{}", self.0)
1883 /// }
1884 /// }
1885 ///
1886 /// assert_eq!(format!("{:04}", Foo(23)), "23");
1887 /// ```
1888 #[must_use]
1889 #[stable(feature = "fmt_flags", since = "1.5.0")]
1890 pub fn sign_aware_zero_pad(&self) -> bool {
1891 self.flags & (1 << rt::Flag::SignAwareZeroPad as u32) != 0
1892 }
1893
1894 // FIXME: Decide what public API we want for these two flags.
1895 // https://github.com/rust-lang/rust/issues/48584
1896 fn debug_lower_hex(&self) -> bool {
1897 self.flags & (1 << rt::Flag::DebugLowerHex as u32) != 0
1898 }
1899
1900 fn debug_upper_hex(&self) -> bool {
1901 self.flags & (1 << rt::Flag::DebugUpperHex as u32) != 0
1902 }
1903
1904 /// Creates a [`DebugStruct`] builder designed to assist with creation of
1905 /// [`fmt::Debug`] implementations for structs.
1906 ///
1907 /// [`fmt::Debug`]: self::Debug
1908 ///
1909 /// # Examples
1910 ///
1911 /// ```rust
1912 /// use std::fmt;
1913 /// use std::net::Ipv4Addr;
1914 ///
1915 /// struct Foo {
1916 /// bar: i32,
1917 /// baz: String,
1918 /// addr: Ipv4Addr,
1919 /// }
1920 ///
1921 /// impl fmt::Debug for Foo {
1922 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1923 /// fmt.debug_struct("Foo")
1924 /// .field("bar", &self.bar)
1925 /// .field("baz", &self.baz)
1926 /// .field("addr", &format_args!("{}", self.addr))
1927 /// .finish()
1928 /// }
1929 /// }
1930 ///
1931 /// assert_eq!(
1932 /// "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
1933 /// format!("{:?}", Foo {
1934 /// bar: 10,
1935 /// baz: "Hello World".to_string(),
1936 /// addr: Ipv4Addr::new(127, 0, 0, 1),
1937 /// })
1938 /// );
1939 /// ```
1940 #[stable(feature = "debug_builders", since = "1.2.0")]
1941 pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
1942 builders::debug_struct_new(self, name)
1943 }
1944
1945 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
1946 /// `debug_struct_fields_finish` is more general, but this is faster for 1 field.
1947 #[doc(hidden)]
1948 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
1949 pub fn debug_struct_field1_finish<'b>(
1950 &'b mut self,
1951 name: &str,
1952 name1: &str,
1953 value1: &dyn Debug,
1954 ) -> Result {
1955 let mut builder = builders::debug_struct_new(self, name);
1956 builder.field(name1, value1);
1957 builder.finish()
1958 }
1959
1960 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
1961 /// `debug_struct_fields_finish` is more general, but this is faster for 2 fields.
1962 #[doc(hidden)]
1963 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
1964 pub fn debug_struct_field2_finish<'b>(
1965 &'b mut self,
1966 name: &str,
1967 name1: &str,
1968 value1: &dyn Debug,
1969 name2: &str,
1970 value2: &dyn Debug,
1971 ) -> Result {
1972 let mut builder = builders::debug_struct_new(self, name);
1973 builder.field(name1, value1);
1974 builder.field(name2, value2);
1975 builder.finish()
1976 }
1977
1978 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
1979 /// `debug_struct_fields_finish` is more general, but this is faster for 3 fields.
1980 #[doc(hidden)]
1981 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
1982 pub fn debug_struct_field3_finish<'b>(
1983 &'b mut self,
1984 name: &str,
1985 name1: &str,
1986 value1: &dyn Debug,
1987 name2: &str,
1988 value2: &dyn Debug,
1989 name3: &str,
1990 value3: &dyn Debug,
1991 ) -> Result {
1992 let mut builder = builders::debug_struct_new(self, name);
1993 builder.field(name1, value1);
1994 builder.field(name2, value2);
1995 builder.field(name3, value3);
1996 builder.finish()
1997 }
1998
1999 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2000 /// `debug_struct_fields_finish` is more general, but this is faster for 4 fields.
2001 #[doc(hidden)]
2002 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2003 pub fn debug_struct_field4_finish<'b>(
2004 &'b mut self,
2005 name: &str,
2006 name1: &str,
2007 value1: &dyn Debug,
2008 name2: &str,
2009 value2: &dyn Debug,
2010 name3: &str,
2011 value3: &dyn Debug,
2012 name4: &str,
2013 value4: &dyn Debug,
2014 ) -> Result {
2015 let mut builder = builders::debug_struct_new(self, name);
2016 builder.field(name1, value1);
2017 builder.field(name2, value2);
2018 builder.field(name3, value3);
2019 builder.field(name4, value4);
2020 builder.finish()
2021 }
2022
2023 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2024 /// `debug_struct_fields_finish` is more general, but this is faster for 5 fields.
2025 #[doc(hidden)]
2026 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2027 pub fn debug_struct_field5_finish<'b>(
2028 &'b mut self,
2029 name: &str,
2030 name1: &str,
2031 value1: &dyn Debug,
2032 name2: &str,
2033 value2: &dyn Debug,
2034 name3: &str,
2035 value3: &dyn Debug,
2036 name4: &str,
2037 value4: &dyn Debug,
2038 name5: &str,
2039 value5: &dyn Debug,
2040 ) -> Result {
2041 let mut builder = builders::debug_struct_new(self, name);
2042 builder.field(name1, value1);
2043 builder.field(name2, value2);
2044 builder.field(name3, value3);
2045 builder.field(name4, value4);
2046 builder.field(name5, value5);
2047 builder.finish()
2048 }
2049
2050 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2051 /// For the cases not covered by `debug_struct_field[12345]_finish`.
2052 #[doc(hidden)]
2053 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2054 pub fn debug_struct_fields_finish<'b>(
2055 &'b mut self,
2056 name: &str,
2057 names: &[&str],
2058 values: &[&dyn Debug],
2059 ) -> Result {
2060 assert_eq!(names.len(), values.len());
2061 let mut builder = builders::debug_struct_new(self, name);
2062 for (name, value) in iter::zip(names, values) {
2063 builder.field(name, value);
2064 }
2065 builder.finish()
2066 }
2067
2068 /// Creates a `DebugTuple` builder designed to assist with creation of
2069 /// `fmt::Debug` implementations for tuple structs.
2070 ///
2071 /// # Examples
2072 ///
2073 /// ```rust
2074 /// use std::fmt;
2075 /// use std::marker::PhantomData;
2076 ///
2077 /// struct Foo<T>(i32, String, PhantomData<T>);
2078 ///
2079 /// impl<T> fmt::Debug for Foo<T> {
2080 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2081 /// fmt.debug_tuple("Foo")
2082 /// .field(&self.0)
2083 /// .field(&self.1)
2084 /// .field(&format_args!("_"))
2085 /// .finish()
2086 /// }
2087 /// }
2088 ///
2089 /// assert_eq!(
2090 /// "Foo(10, \"Hello\", _)",
2091 /// format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
2092 /// );
2093 /// ```
2094 #[stable(feature = "debug_builders", since = "1.2.0")]
2095 pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
2096 builders::debug_tuple_new(self, name)
2097 }
2098
2099 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2100 /// `debug_tuple_fields_finish` is more general, but this is faster for 1 field.
2101 #[doc(hidden)]
2102 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2103 pub fn debug_tuple_field1_finish<'b>(&'b mut self, name: &str, value1: &dyn Debug) -> Result {
2104 let mut builder = builders::debug_tuple_new(self, name);
2105 builder.field(value1);
2106 builder.finish()
2107 }
2108
2109 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2110 /// `debug_tuple_fields_finish` is more general, but this is faster for 2 fields.
2111 #[doc(hidden)]
2112 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2113 pub fn debug_tuple_field2_finish<'b>(
2114 &'b mut self,
2115 name: &str,
2116 value1: &dyn Debug,
2117 value2: &dyn Debug,
2118 ) -> Result {
2119 let mut builder = builders::debug_tuple_new(self, name);
2120 builder.field(value1);
2121 builder.field(value2);
2122 builder.finish()
2123 }
2124
2125 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2126 /// `debug_tuple_fields_finish` is more general, but this is faster for 3 fields.
2127 #[doc(hidden)]
2128 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2129 pub fn debug_tuple_field3_finish<'b>(
2130 &'b mut self,
2131 name: &str,
2132 value1: &dyn Debug,
2133 value2: &dyn Debug,
2134 value3: &dyn Debug,
2135 ) -> Result {
2136 let mut builder = builders::debug_tuple_new(self, name);
2137 builder.field(value1);
2138 builder.field(value2);
2139 builder.field(value3);
2140 builder.finish()
2141 }
2142
2143 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2144 /// `debug_tuple_fields_finish` is more general, but this is faster for 4 fields.
2145 #[doc(hidden)]
2146 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2147 pub fn debug_tuple_field4_finish<'b>(
2148 &'b mut self,
2149 name: &str,
2150 value1: &dyn Debug,
2151 value2: &dyn Debug,
2152 value3: &dyn Debug,
2153 value4: &dyn Debug,
2154 ) -> Result {
2155 let mut builder = builders::debug_tuple_new(self, name);
2156 builder.field(value1);
2157 builder.field(value2);
2158 builder.field(value3);
2159 builder.field(value4);
2160 builder.finish()
2161 }
2162
2163 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2164 /// `debug_tuple_fields_finish` is more general, but this is faster for 5 fields.
2165 #[doc(hidden)]
2166 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2167 pub fn debug_tuple_field5_finish<'b>(
2168 &'b mut self,
2169 name: &str,
2170 value1: &dyn Debug,
2171 value2: &dyn Debug,
2172 value3: &dyn Debug,
2173 value4: &dyn Debug,
2174 value5: &dyn Debug,
2175 ) -> Result {
2176 let mut builder = builders::debug_tuple_new(self, name);
2177 builder.field(value1);
2178 builder.field(value2);
2179 builder.field(value3);
2180 builder.field(value4);
2181 builder.field(value5);
2182 builder.finish()
2183 }
2184
2185 /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
2186 /// For the cases not covered by `debug_tuple_field[12345]_finish`.
2187 #[doc(hidden)]
2188 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2189 pub fn debug_tuple_fields_finish<'b>(
2190 &'b mut self,
2191 name: &str,
2192 values: &[&dyn Debug],
2193 ) -> Result {
2194 let mut builder = builders::debug_tuple_new(self, name);
2195 for value in values {
2196 builder.field(value);
2197 }
2198 builder.finish()
2199 }
2200
2201 /// Creates a `DebugList` builder designed to assist with creation of
2202 /// `fmt::Debug` implementations for list-like structures.
2203 ///
2204 /// # Examples
2205 ///
2206 /// ```rust
2207 /// use std::fmt;
2208 ///
2209 /// struct Foo(Vec<i32>);
2210 ///
2211 /// impl fmt::Debug for Foo {
2212 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2213 /// fmt.debug_list().entries(self.0.iter()).finish()
2214 /// }
2215 /// }
2216 ///
2217 /// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "[10, 11]");
2218 /// ```
2219 #[stable(feature = "debug_builders", since = "1.2.0")]
2220 pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
2221 builders::debug_list_new(self)
2222 }
2223
2224 /// Creates a `DebugSet` builder designed to assist with creation of
2225 /// `fmt::Debug` implementations for set-like structures.
2226 ///
2227 /// # Examples
2228 ///
2229 /// ```rust
2230 /// use std::fmt;
2231 ///
2232 /// struct Foo(Vec<i32>);
2233 ///
2234 /// impl fmt::Debug for Foo {
2235 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2236 /// fmt.debug_set().entries(self.0.iter()).finish()
2237 /// }
2238 /// }
2239 ///
2240 /// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "{10, 11}");
2241 /// ```
2242 ///
2243 /// [`format_args!`]: crate::format_args
2244 ///
2245 /// In this more complex example, we use [`format_args!`] and `.debug_set()`
2246 /// to build a list of match arms:
2247 ///
2248 /// ```rust
2249 /// use std::fmt;
2250 ///
2251 /// struct Arm<'a, L, R>(&'a (L, R));
2252 /// struct Table<'a, K, V>(&'a [(K, V)], V);
2253 ///
2254 /// impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
2255 /// where
2256 /// L: 'a + fmt::Debug, R: 'a + fmt::Debug
2257 /// {
2258 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2259 /// L::fmt(&(self.0).0, fmt)?;
2260 /// fmt.write_str(" => ")?;
2261 /// R::fmt(&(self.0).1, fmt)
2262 /// }
2263 /// }
2264 ///
2265 /// impl<'a, K, V> fmt::Debug for Table<'a, K, V>
2266 /// where
2267 /// K: 'a + fmt::Debug, V: 'a + fmt::Debug
2268 /// {
2269 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2270 /// fmt.debug_set()
2271 /// .entries(self.0.iter().map(Arm))
2272 /// .entry(&Arm(&(format_args!("_"), &self.1)))
2273 /// .finish()
2274 /// }
2275 /// }
2276 /// ```
2277 #[stable(feature = "debug_builders", since = "1.2.0")]
2278 pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
2279 builders::debug_set_new(self)
2280 }
2281
2282 /// Creates a `DebugMap` builder designed to assist with creation of
2283 /// `fmt::Debug` implementations for map-like structures.
2284 ///
2285 /// # Examples
2286 ///
2287 /// ```rust
2288 /// use std::fmt;
2289 ///
2290 /// struct Foo(Vec<(String, i32)>);
2291 ///
2292 /// impl fmt::Debug for Foo {
2293 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2294 /// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
2295 /// }
2296 /// }
2297 ///
2298 /// assert_eq!(
2299 /// format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
2300 /// r#"{"A": 10, "B": 11}"#
2301 /// );
2302 /// ```
2303 #[stable(feature = "debug_builders", since = "1.2.0")]
2304 pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
2305 builders::debug_map_new(self)
2306 }
2307}
2308
2309#[stable(since = "1.2.0", feature = "formatter_write")]
2310impl Write for Formatter<'_> {
2311 fn write_str(&mut self, s: &str) -> Result {
2312 self.buf.write_str(s)
2313 }
2314
2315 fn write_char(&mut self, c: char) -> Result {
2316 self.buf.write_char(c)
2317 }
2318
2319 #[inline]
2320 fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
2321 if let Some(s: &str) = args.as_statically_known_str() {
2322 self.buf.write_str(s)
2323 } else {
2324 write(self.buf, args)
2325 }
2326 }
2327}
2328
2329#[stable(feature = "rust1", since = "1.0.0")]
2330impl Display for Error {
2331 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2332 Display::fmt(self:"an error occurred when formatting an argument", f)
2333 }
2334}
2335
2336// Implementations of the core formatting traits
2337
2338macro_rules! fmt_refs {
2339 ($($tr:ident),*) => {
2340 $(
2341 #[stable(feature = "rust1", since = "1.0.0")]
2342 impl<T: ?Sized + $tr> $tr for &T {
2343 fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
2344 }
2345 #[stable(feature = "rust1", since = "1.0.0")]
2346 impl<T: ?Sized + $tr> $tr for &mut T {
2347 fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
2348 }
2349 )*
2350 }
2351}
2352
2353fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
2354
2355#[unstable(feature = "never_type", issue = "35121")]
2356impl Debug for ! {
2357 #[inline]
2358 fn fmt(&self, _: &mut Formatter<'_>) -> Result {
2359 *self
2360 }
2361}
2362
2363#[unstable(feature = "never_type", issue = "35121")]
2364impl Display for ! {
2365 #[inline]
2366 fn fmt(&self, _: &mut Formatter<'_>) -> Result {
2367 *self
2368 }
2369}
2370
2371#[stable(feature = "rust1", since = "1.0.0")]
2372impl Debug for bool {
2373 #[inline]
2374 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2375 Display::fmt(self, f)
2376 }
2377}
2378
2379#[stable(feature = "rust1", since = "1.0.0")]
2380impl Display for bool {
2381 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2382 Display::fmt(self:if *self { "true" } else { "false" }, f)
2383 }
2384}
2385
2386#[stable(feature = "rust1", since = "1.0.0")]
2387impl Debug for str {
2388 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2389 f.write_char('"')?;
2390 let mut from: usize = 0;
2391 for (i: usize, c: char) in self.char_indices() {
2392 let esc: EscapeDebug = c.escape_debug_ext(args:EscapeDebugExtArgs {
2393 escape_grapheme_extended: true,
2394 escape_single_quote: false,
2395 escape_double_quote: true,
2396 });
2397 // If char needs escaping, flush backlog so far and write, else skip
2398 if esc.len() != 1 {
2399 f.write_str(&self[from..i])?;
2400 for c: char in esc {
2401 f.write_char(c)?;
2402 }
2403 from = i + c.len_utf8();
2404 }
2405 }
2406 f.write_str(&self[from..])?;
2407 f.write_char('"')
2408 }
2409}
2410
2411#[stable(feature = "rust1", since = "1.0.0")]
2412impl Display for str {
2413 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2414 f.pad(self)
2415 }
2416}
2417
2418#[stable(feature = "rust1", since = "1.0.0")]
2419impl Debug for char {
2420 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2421 f.write_char('\'')?;
2422 for c: char in self.escape_debug_ext(args:EscapeDebugExtArgs {
2423 escape_grapheme_extended: true,
2424 escape_single_quote: true,
2425 escape_double_quote: false,
2426 }) {
2427 f.write_char(c)?
2428 }
2429 f.write_char('\'')
2430 }
2431}
2432
2433#[stable(feature = "rust1", since = "1.0.0")]
2434impl Display for char {
2435 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2436 if f.width.is_none() && f.precision.is_none() {
2437 f.write_char(*self)
2438 } else {
2439 f.pad(self.encode_utf8(&mut [0; 4]))
2440 }
2441 }
2442}
2443
2444#[stable(feature = "rust1", since = "1.0.0")]
2445impl<T: ?Sized> Pointer for *const T {
2446 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2447 // Cast is needed here because `.expose_provenance()` requires `T: Sized`.
2448 pointer_fmt_inner((*self as *const ()).expose_provenance(), f)
2449 }
2450}
2451
2452/// Since the formatting will be identical for all pointer types, use a non-monomorphized
2453/// implementation for the actual formatting to reduce the amount of codegen work needed.
2454///
2455/// This uses `ptr_addr: usize` and not `ptr: *const ()` to be able to use this for
2456/// `fn(...) -> ...` without using [problematic] "Oxford Casts".
2457///
2458/// [problematic]: https://github.com/rust-lang/rust/issues/95489
2459pub(crate) fn pointer_fmt_inner(ptr_addr: usize, f: &mut Formatter<'_>) -> Result {
2460 let old_width: Option = f.width;
2461 let old_flags: u32 = f.flags;
2462
2463 // The alternate flag is already treated by LowerHex as being special-
2464 // it denotes whether to prefix with 0x. We use it to work out whether
2465 // or not to zero extend, and then unconditionally set it to get the
2466 // prefix.
2467 if f.alternate() {
2468 f.flags |= 1 << (rt::Flag::SignAwareZeroPad as u32);
2469
2470 if f.width.is_none() {
2471 f.width = Some((usize::BITS / 4) as usize + 2);
2472 }
2473 }
2474 f.flags |= 1 << (rt::Flag::Alternate as u32);
2475
2476 let ret: Result<(), Error> = LowerHex::fmt(&ptr_addr, f);
2477
2478 f.width = old_width;
2479 f.flags = old_flags;
2480
2481 ret
2482}
2483
2484#[stable(feature = "rust1", since = "1.0.0")]
2485impl<T: ?Sized> Pointer for *mut T {
2486 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2487 Pointer::fmt(&(*self as *const T), f)
2488 }
2489}
2490
2491#[stable(feature = "rust1", since = "1.0.0")]
2492impl<T: ?Sized> Pointer for &T {
2493 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2494 Pointer::fmt(&(*self as *const T), f)
2495 }
2496}
2497
2498#[stable(feature = "rust1", since = "1.0.0")]
2499impl<T: ?Sized> Pointer for &mut T {
2500 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2501 Pointer::fmt(&(&**self as *const T), f)
2502 }
2503}
2504
2505// Implementation of Display/Debug for various core types
2506
2507#[stable(feature = "rust1", since = "1.0.0")]
2508impl<T: ?Sized> Debug for *const T {
2509 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2510 Pointer::fmt(self, f)
2511 }
2512}
2513#[stable(feature = "rust1", since = "1.0.0")]
2514impl<T: ?Sized> Debug for *mut T {
2515 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2516 Pointer::fmt(self, f)
2517 }
2518}
2519
2520macro_rules! peel {
2521 ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
2522}
2523
2524macro_rules! tuple {
2525 () => ();
2526 ( $($name:ident,)+ ) => (
2527 maybe_tuple_doc! {
2528 $($name)+ @
2529 #[stable(feature = "rust1", since = "1.0.0")]
2530 impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
2531 #[allow(non_snake_case, unused_assignments)]
2532 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2533 let mut builder = f.debug_tuple("");
2534 let ($(ref $name,)+) = *self;
2535 $(
2536 builder.field(&$name);
2537 )+
2538
2539 builder.finish()
2540 }
2541 }
2542 }
2543 peel! { $($name,)+ }
2544 )
2545}
2546
2547macro_rules! maybe_tuple_doc {
2548 ($a:ident @ #[$meta:meta] $item:item) => {
2549 #[doc(fake_variadic)]
2550 #[doc = "This trait is implemented for tuples up to twelve items long."]
2551 #[$meta]
2552 $item
2553 };
2554 ($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
2555 #[doc(hidden)]
2556 #[$meta]
2557 $item
2558 };
2559}
2560
2561macro_rules! last_type {
2562 ($a:ident,) => { $a };
2563 ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
2564}
2565
2566tuple! { E, D, C, B, A, Z, Y, X, W, V, U, T, }
2567
2568#[stable(feature = "rust1", since = "1.0.0")]
2569impl<T: Debug> Debug for [T] {
2570 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2571 f.debug_list().entries(self.iter()).finish()
2572 }
2573}
2574
2575#[stable(feature = "rust1", since = "1.0.0")]
2576impl Debug for () {
2577 #[inline]
2578 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2579 f.pad("()")
2580 }
2581}
2582#[stable(feature = "rust1", since = "1.0.0")]
2583impl<T: ?Sized> Debug for PhantomData<T> {
2584 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2585 write!(f, "PhantomData<{}>", crate::any::type_name::<T>())
2586 }
2587}
2588
2589#[stable(feature = "rust1", since = "1.0.0")]
2590impl<T: Copy + Debug> Debug for Cell<T> {
2591 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2592 f.debug_struct("Cell").field(name:"value", &self.get()).finish()
2593 }
2594}
2595
2596#[stable(feature = "rust1", since = "1.0.0")]
2597impl<T: ?Sized + Debug> Debug for RefCell<T> {
2598 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2599 let mut d: DebugStruct<'_, '_> = f.debug_struct(name:"RefCell");
2600 match self.try_borrow() {
2601 Ok(borrow: Ref<'_, T>) => d.field(name:"value", &borrow),
2602 Err(_) => d.field(name:"value", &format_args!("<borrowed>")),
2603 };
2604 d.finish()
2605 }
2606}
2607
2608#[stable(feature = "rust1", since = "1.0.0")]
2609impl<T: ?Sized + Debug> Debug for Ref<'_, T> {
2610 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2611 Debug::fmt(&**self, f)
2612 }
2613}
2614
2615#[stable(feature = "rust1", since = "1.0.0")]
2616impl<T: ?Sized + Debug> Debug for RefMut<'_, T> {
2617 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2618 Debug::fmt(&*(self.deref()), f)
2619 }
2620}
2621
2622#[stable(feature = "core_impl_debug", since = "1.9.0")]
2623impl<T: ?Sized> Debug for UnsafeCell<T> {
2624 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2625 f.debug_struct(name:"UnsafeCell").finish_non_exhaustive()
2626 }
2627}
2628
2629#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
2630impl<T: ?Sized> Debug for SyncUnsafeCell<T> {
2631 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2632 f.debug_struct(name:"SyncUnsafeCell").finish_non_exhaustive()
2633 }
2634}
2635
2636// If you expected tests to be here, look instead at the core/tests/fmt.rs file,
2637// it's a lot easier than creating all of the rt::Piece structures here.
2638// There are also tests in the alloc crate, for those that need allocations.
2639