1//! Utilities for comparing and ordering values.
2//!
3//! This module contains various tools for comparing and ordering values. In
4//! summary:
5//!
6//! * [`PartialEq<Rhs>`] overloads the `==` and `!=` operators. In cases where
7//! `Rhs` (the right hand side's type) is `Self`, this trait corresponds to a
8//! partial equivalence relation.
9//! * [`Eq`] indicates that the overloaded `==` operator corresponds to an
10//! equivalence relation.
11//! * [`Ord`] and [`PartialOrd`] are traits that allow you to define total and
12//! partial orderings between values, respectively. Implementing them overloads
13//! the `<`, `<=`, `>`, and `>=` operators.
14//! * [`Ordering`] is an enum returned by the main functions of [`Ord`] and
15//! [`PartialOrd`], and describes an ordering of two values (less, equal, or
16//! greater).
17//! * [`Reverse`] is a struct that allows you to easily reverse an ordering.
18//! * [`max`] and [`min`] are functions that build off of [`Ord`] and allow you
19//! to find the maximum or minimum of two values.
20//!
21//! For more details, see the respective documentation of each item in the list.
22//!
23//! [`max`]: Ord::max
24//! [`min`]: Ord::min
25
26#![stable(feature = "rust1", since = "1.0.0")]
27
28mod bytewise;
29pub(crate) use bytewise::BytewiseEq;
30
31use self::Ordering::*;
32use crate::ops::ControlFlow;
33
34/// Trait for comparisons using the equality operator.
35///
36/// Implementing this trait for types provides the `==` and `!=` operators for
37/// those types.
38///
39/// `x.eq(y)` can also be written `x == y`, and `x.ne(y)` can be written `x != y`.
40/// We use the easier-to-read infix notation in the remainder of this documentation.
41///
42/// This trait allows for comparisons using the equality operator, for types
43/// that do not have a full equivalence relation. For example, in floating point
44/// numbers `NaN != NaN`, so floating point types implement `PartialEq` but not
45/// [`trait@Eq`]. Formally speaking, when `Rhs == Self`, this trait corresponds
46/// to a [partial equivalence relation].
47///
48/// [partial equivalence relation]: https://en.wikipedia.org/wiki/Partial_equivalence_relation
49///
50/// Implementations must ensure that `eq` and `ne` are consistent with each other:
51///
52/// - `a != b` if and only if `!(a == b)`.
53///
54/// The default implementation of `ne` provides this consistency and is almost
55/// always sufficient. It should not be overridden without very good reason.
56///
57/// If [`PartialOrd`] or [`Ord`] are also implemented for `Self` and `Rhs`, their methods must also
58/// be consistent with `PartialEq` (see the documentation of those traits for the exact
59/// requirements). It's easy to accidentally make them disagree by deriving some of the traits and
60/// manually implementing others.
61///
62/// The equality relation `==` must satisfy the following conditions
63/// (for all `a`, `b`, `c` of type `A`, `B`, `C`):
64///
65/// - **Symmetry**: if `A: PartialEq<B>` and `B: PartialEq<A>`, then **`a == b`
66/// implies `b == a`**; and
67///
68/// - **Transitivity**: if `A: PartialEq<B>` and `B: PartialEq<C>` and `A:
69/// PartialEq<C>`, then **`a == b` and `b == c` implies `a == c`**.
70/// This must also work for longer chains, such as when `A: PartialEq<B>`, `B: PartialEq<C>`,
71/// `C: PartialEq<D>`, and `A: PartialEq<D>` all exist.
72///
73/// Note that the `B: PartialEq<A>` (symmetric) and `A: PartialEq<C>`
74/// (transitive) impls are not forced to exist, but these requirements apply
75/// whenever they do exist.
76///
77/// Violating these requirements is a logic error. The behavior resulting from a logic error is not
78/// specified, but users of the trait must ensure that such logic errors do *not* result in
79/// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these
80/// methods.
81///
82/// ## Cross-crate considerations
83///
84/// Upholding the requirements stated above can become tricky when one crate implements `PartialEq`
85/// for a type of another crate (i.e., to allow comparing one of its own types with a type from the
86/// standard library). The recommendation is to never implement this trait for a foreign type. In
87/// other words, such a crate should do `impl PartialEq<ForeignType> for LocalType`, but it should
88/// *not* do `impl PartialEq<LocalType> for ForeignType`.
89///
90/// This avoids the problem of transitive chains that criss-cross crate boundaries: for all local
91/// types `T`, you may assume that no other crate will add `impl`s that allow comparing `T == U`. In
92/// other words, if other crates add `impl`s that allow building longer transitive chains `U1 == ...
93/// == T == V1 == ...`, then all the types that appear to the right of `T` must be types that the
94/// crate defining `T` already knows about. This rules out transitive chains where downstream crates
95/// can add new `impl`s that "stitch together" comparisons of foreign types in ways that violate
96/// transitivity.
97///
98/// Not having such foreign `impl`s also avoids forward compatibility issues where one crate adding
99/// more `PartialEq` implementations can cause build failures in downstream crates.
100///
101/// ## Derivable
102///
103/// This trait can be used with `#[derive]`. When `derive`d on structs, two
104/// instances are equal if all fields are equal, and not equal if any fields
105/// are not equal. When `derive`d on enums, two instances are equal if they
106/// are the same variant and all fields are equal.
107///
108/// ## How can I implement `PartialEq`?
109///
110/// An example implementation for a domain in which two books are considered
111/// the same book if their ISBN matches, even if the formats differ:
112///
113/// ```
114/// enum BookFormat {
115/// Paperback,
116/// Hardback,
117/// Ebook,
118/// }
119///
120/// struct Book {
121/// isbn: i32,
122/// format: BookFormat,
123/// }
124///
125/// impl PartialEq for Book {
126/// fn eq(&self, other: &Self) -> bool {
127/// self.isbn == other.isbn
128/// }
129/// }
130///
131/// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
132/// let b2 = Book { isbn: 3, format: BookFormat::Ebook };
133/// let b3 = Book { isbn: 10, format: BookFormat::Paperback };
134///
135/// assert!(b1 == b2);
136/// assert!(b1 != b3);
137/// ```
138///
139/// ## How can I compare two different types?
140///
141/// The type you can compare with is controlled by `PartialEq`'s type parameter.
142/// For example, let's tweak our previous code a bit:
143///
144/// ```
145/// // The derive implements <BookFormat> == <BookFormat> comparisons
146/// #[derive(PartialEq)]
147/// enum BookFormat {
148/// Paperback,
149/// Hardback,
150/// Ebook,
151/// }
152///
153/// struct Book {
154/// isbn: i32,
155/// format: BookFormat,
156/// }
157///
158/// // Implement <Book> == <BookFormat> comparisons
159/// impl PartialEq<BookFormat> for Book {
160/// fn eq(&self, other: &BookFormat) -> bool {
161/// self.format == *other
162/// }
163/// }
164///
165/// // Implement <BookFormat> == <Book> comparisons
166/// impl PartialEq<Book> for BookFormat {
167/// fn eq(&self, other: &Book) -> bool {
168/// *self == other.format
169/// }
170/// }
171///
172/// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
173///
174/// assert!(b1 == BookFormat::Paperback);
175/// assert!(BookFormat::Ebook != b1);
176/// ```
177///
178/// By changing `impl PartialEq for Book` to `impl PartialEq<BookFormat> for Book`,
179/// we allow `BookFormat`s to be compared with `Book`s.
180///
181/// A comparison like the one above, which ignores some fields of the struct,
182/// can be dangerous. It can easily lead to an unintended violation of the
183/// requirements for a partial equivalence relation. For example, if we kept
184/// the above implementation of `PartialEq<Book>` for `BookFormat` and added an
185/// implementation of `PartialEq<Book>` for `Book` (either via a `#[derive]` or
186/// via the manual implementation from the first example) then the result would
187/// violate transitivity:
188///
189/// ```should_panic
190/// #[derive(PartialEq)]
191/// enum BookFormat {
192/// Paperback,
193/// Hardback,
194/// Ebook,
195/// }
196///
197/// #[derive(PartialEq)]
198/// struct Book {
199/// isbn: i32,
200/// format: BookFormat,
201/// }
202///
203/// impl PartialEq<BookFormat> for Book {
204/// fn eq(&self, other: &BookFormat) -> bool {
205/// self.format == *other
206/// }
207/// }
208///
209/// impl PartialEq<Book> for BookFormat {
210/// fn eq(&self, other: &Book) -> bool {
211/// *self == other.format
212/// }
213/// }
214///
215/// fn main() {
216/// let b1 = Book { isbn: 1, format: BookFormat::Paperback };
217/// let b2 = Book { isbn: 2, format: BookFormat::Paperback };
218///
219/// assert!(b1 == BookFormat::Paperback);
220/// assert!(BookFormat::Paperback == b2);
221///
222/// // The following should hold by transitivity but doesn't.
223/// assert!(b1 == b2); // <-- PANICS
224/// }
225/// ```
226///
227/// # Examples
228///
229/// ```
230/// let x: u32 = 0;
231/// let y: u32 = 1;
232///
233/// assert_eq!(x == y, false);
234/// assert_eq!(x.eq(&y), false);
235/// ```
236///
237/// [`eq`]: PartialEq::eq
238/// [`ne`]: PartialEq::ne
239#[lang = "eq"]
240#[stable(feature = "rust1", since = "1.0.0")]
241#[doc(alias = "==")]
242#[doc(alias = "!=")]
243#[rustc_on_unimplemented(
244 message = "can't compare `{Self}` with `{Rhs}`",
245 label = "no implementation for `{Self} == {Rhs}`",
246 append_const_msg
247)]
248#[rustc_diagnostic_item = "PartialEq"]
249pub trait PartialEq<Rhs: ?Sized = Self> {
250 /// Tests for `self` and `other` values to be equal, and is used by `==`.
251 #[must_use]
252 #[stable(feature = "rust1", since = "1.0.0")]
253 #[rustc_diagnostic_item = "cmp_partialeq_eq"]
254 fn eq(&self, other: &Rhs) -> bool;
255
256 /// Tests for `!=`. The default implementation is almost always sufficient,
257 /// and should not be overridden without very good reason.
258 #[inline]
259 #[must_use]
260 #[stable(feature = "rust1", since = "1.0.0")]
261 #[rustc_diagnostic_item = "cmp_partialeq_ne"]
262 fn ne(&self, other: &Rhs) -> bool {
263 !self.eq(other)
264 }
265}
266
267/// Derive macro generating an impl of the trait [`PartialEq`].
268/// The behavior of this macro is described in detail [here](PartialEq#derivable).
269#[rustc_builtin_macro]
270#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
271#[allow_internal_unstable(core_intrinsics, structural_match)]
272pub macro PartialEq($item:item) {
273 /* compiler built-in */
274}
275
276/// Trait for comparisons corresponding to [equivalence relations](
277/// https://en.wikipedia.org/wiki/Equivalence_relation).
278///
279/// The primary difference to [`PartialEq`] is the additional requirement for reflexivity. A type
280/// that implements [`PartialEq`] guarantees that for all `a`, `b` and `c`:
281///
282/// - symmetric: `a == b` implies `b == a` and `a != b` implies `!(a == b)`
283/// - transitive: `a == b` and `b == c` implies `a == c`
284///
285/// `Eq`, which builds on top of [`PartialEq`] also implies:
286///
287/// - reflexive: `a == a`
288///
289/// This property cannot be checked by the compiler, and therefore `Eq` is a trait without methods.
290///
291/// Violating this property is a logic error. The behavior resulting from a logic error is not
292/// specified, but users of the trait must ensure that such logic errors do *not* result in
293/// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these
294/// methods.
295///
296/// Floating point types such as [`f32`] and [`f64`] implement only [`PartialEq`] but *not* `Eq`
297/// because `NaN` != `NaN`.
298///
299/// ## Derivable
300///
301/// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has no extra methods, it
302/// is only informing the compiler that this is an equivalence relation rather than a partial
303/// equivalence relation. Note that the `derive` strategy requires all fields are `Eq`, which isn't
304/// always desired.
305///
306/// ## How can I implement `Eq`?
307///
308/// If you cannot use the `derive` strategy, specify that your type implements `Eq`, which has no
309/// extra methods:
310///
311/// ```
312/// enum BookFormat {
313/// Paperback,
314/// Hardback,
315/// Ebook,
316/// }
317///
318/// struct Book {
319/// isbn: i32,
320/// format: BookFormat,
321/// }
322///
323/// impl PartialEq for Book {
324/// fn eq(&self, other: &Self) -> bool {
325/// self.isbn == other.isbn
326/// }
327/// }
328///
329/// impl Eq for Book {}
330/// ```
331#[doc(alias = "==")]
332#[doc(alias = "!=")]
333#[stable(feature = "rust1", since = "1.0.0")]
334#[rustc_diagnostic_item = "Eq"]
335pub trait Eq: PartialEq<Self> {
336 // this method is used solely by `impl Eq or #[derive(Eq)]` to assert that every component of a
337 // type implements `Eq` itself. The current deriving infrastructure means doing this assertion
338 // without using a method on this trait is nearly impossible.
339 //
340 // This should never be implemented by hand.
341 #[doc(hidden)]
342 #[coverage(off)]
343 #[inline]
344 #[stable(feature = "rust1", since = "1.0.0")]
345 fn assert_receiver_is_total_eq(&self) {}
346}
347
348/// Derive macro generating an impl of the trait [`Eq`].
349#[rustc_builtin_macro]
350#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
351#[allow_internal_unstable(core_intrinsics, derive_eq, structural_match)]
352#[allow_internal_unstable(coverage_attribute)]
353pub macro Eq($item:item) {
354 /* compiler built-in */
355}
356
357// FIXME: this struct is used solely by #[derive] to
358// assert that every component of a type implements Eq.
359//
360// This struct should never appear in user code.
361#[doc(hidden)]
362#[allow(missing_debug_implementations)]
363#[unstable(feature = "derive_eq", reason = "deriving hack, should not be public", issue = "none")]
364pub struct AssertParamIsEq<T: Eq + ?Sized> {
365 _field: crate::marker::PhantomData<T>,
366}
367
368/// An `Ordering` is the result of a comparison between two values.
369///
370/// # Examples
371///
372/// ```
373/// use std::cmp::Ordering;
374///
375/// assert_eq!(1.cmp(&2), Ordering::Less);
376///
377/// assert_eq!(1.cmp(&1), Ordering::Equal);
378///
379/// assert_eq!(2.cmp(&1), Ordering::Greater);
380/// ```
381#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
382#[stable(feature = "rust1", since = "1.0.0")]
383// This is a lang item only so that `BinOp::Cmp` in MIR can return it.
384// It has no special behavior, but does require that the three variants
385// `Less`/`Equal`/`Greater` remain `-1_i8`/`0_i8`/`+1_i8` respectively.
386#[lang = "Ordering"]
387#[repr(i8)]
388pub enum Ordering {
389 /// An ordering where a compared value is less than another.
390 #[stable(feature = "rust1", since = "1.0.0")]
391 Less = -1,
392 /// An ordering where a compared value is equal to another.
393 #[stable(feature = "rust1", since = "1.0.0")]
394 Equal = 0,
395 /// An ordering where a compared value is greater than another.
396 #[stable(feature = "rust1", since = "1.0.0")]
397 Greater = 1,
398}
399
400impl Ordering {
401 #[inline]
402 const fn as_raw(self) -> i8 {
403 // FIXME(const-hack): just use `PartialOrd` against `Equal` once that's const
404 crate::intrinsics::discriminant_value(&self)
405 }
406
407 /// Returns `true` if the ordering is the `Equal` variant.
408 ///
409 /// # Examples
410 ///
411 /// ```
412 /// use std::cmp::Ordering;
413 ///
414 /// assert_eq!(Ordering::Less.is_eq(), false);
415 /// assert_eq!(Ordering::Equal.is_eq(), true);
416 /// assert_eq!(Ordering::Greater.is_eq(), false);
417 /// ```
418 #[inline]
419 #[must_use]
420 #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
421 #[stable(feature = "ordering_helpers", since = "1.53.0")]
422 pub const fn is_eq(self) -> bool {
423 // All the `is_*` methods are implemented as comparisons against zero
424 // to follow how clang's libcxx implements their equivalents in
425 // <https://github.com/llvm/llvm-project/blob/60486292b79885b7800b082754153202bef5b1f0/libcxx/include/__compare/is_eq.h#L23-L28>
426
427 self.as_raw() == 0
428 }
429
430 /// Returns `true` if the ordering is not the `Equal` variant.
431 ///
432 /// # Examples
433 ///
434 /// ```
435 /// use std::cmp::Ordering;
436 ///
437 /// assert_eq!(Ordering::Less.is_ne(), true);
438 /// assert_eq!(Ordering::Equal.is_ne(), false);
439 /// assert_eq!(Ordering::Greater.is_ne(), true);
440 /// ```
441 #[inline]
442 #[must_use]
443 #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
444 #[stable(feature = "ordering_helpers", since = "1.53.0")]
445 pub const fn is_ne(self) -> bool {
446 self.as_raw() != 0
447 }
448
449 /// Returns `true` if the ordering is the `Less` variant.
450 ///
451 /// # Examples
452 ///
453 /// ```
454 /// use std::cmp::Ordering;
455 ///
456 /// assert_eq!(Ordering::Less.is_lt(), true);
457 /// assert_eq!(Ordering::Equal.is_lt(), false);
458 /// assert_eq!(Ordering::Greater.is_lt(), false);
459 /// ```
460 #[inline]
461 #[must_use]
462 #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
463 #[stable(feature = "ordering_helpers", since = "1.53.0")]
464 pub const fn is_lt(self) -> bool {
465 self.as_raw() < 0
466 }
467
468 /// Returns `true` if the ordering is the `Greater` variant.
469 ///
470 /// # Examples
471 ///
472 /// ```
473 /// use std::cmp::Ordering;
474 ///
475 /// assert_eq!(Ordering::Less.is_gt(), false);
476 /// assert_eq!(Ordering::Equal.is_gt(), false);
477 /// assert_eq!(Ordering::Greater.is_gt(), true);
478 /// ```
479 #[inline]
480 #[must_use]
481 #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
482 #[stable(feature = "ordering_helpers", since = "1.53.0")]
483 pub const fn is_gt(self) -> bool {
484 self.as_raw() > 0
485 }
486
487 /// Returns `true` if the ordering is either the `Less` or `Equal` variant.
488 ///
489 /// # Examples
490 ///
491 /// ```
492 /// use std::cmp::Ordering;
493 ///
494 /// assert_eq!(Ordering::Less.is_le(), true);
495 /// assert_eq!(Ordering::Equal.is_le(), true);
496 /// assert_eq!(Ordering::Greater.is_le(), false);
497 /// ```
498 #[inline]
499 #[must_use]
500 #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
501 #[stable(feature = "ordering_helpers", since = "1.53.0")]
502 pub const fn is_le(self) -> bool {
503 self.as_raw() <= 0
504 }
505
506 /// Returns `true` if the ordering is either the `Greater` or `Equal` variant.
507 ///
508 /// # Examples
509 ///
510 /// ```
511 /// use std::cmp::Ordering;
512 ///
513 /// assert_eq!(Ordering::Less.is_ge(), false);
514 /// assert_eq!(Ordering::Equal.is_ge(), true);
515 /// assert_eq!(Ordering::Greater.is_ge(), true);
516 /// ```
517 #[inline]
518 #[must_use]
519 #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")]
520 #[stable(feature = "ordering_helpers", since = "1.53.0")]
521 pub const fn is_ge(self) -> bool {
522 self.as_raw() >= 0
523 }
524
525 /// Reverses the `Ordering`.
526 ///
527 /// * `Less` becomes `Greater`.
528 /// * `Greater` becomes `Less`.
529 /// * `Equal` becomes `Equal`.
530 ///
531 /// # Examples
532 ///
533 /// Basic behavior:
534 ///
535 /// ```
536 /// use std::cmp::Ordering;
537 ///
538 /// assert_eq!(Ordering::Less.reverse(), Ordering::Greater);
539 /// assert_eq!(Ordering::Equal.reverse(), Ordering::Equal);
540 /// assert_eq!(Ordering::Greater.reverse(), Ordering::Less);
541 /// ```
542 ///
543 /// This method can be used to reverse a comparison:
544 ///
545 /// ```
546 /// let data: &mut [_] = &mut [2, 10, 5, 8];
547 ///
548 /// // sort the array from largest to smallest.
549 /// data.sort_by(|a, b| a.cmp(b).reverse());
550 ///
551 /// let b: &mut [_] = &mut [10, 8, 5, 2];
552 /// assert!(data == b);
553 /// ```
554 #[inline]
555 #[must_use]
556 #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")]
557 #[stable(feature = "rust1", since = "1.0.0")]
558 pub const fn reverse(self) -> Ordering {
559 match self {
560 Less => Greater,
561 Equal => Equal,
562 Greater => Less,
563 }
564 }
565
566 /// Chains two orderings.
567 ///
568 /// Returns `self` when it's not `Equal`. Otherwise returns `other`.
569 ///
570 /// # Examples
571 ///
572 /// ```
573 /// use std::cmp::Ordering;
574 ///
575 /// let result = Ordering::Equal.then(Ordering::Less);
576 /// assert_eq!(result, Ordering::Less);
577 ///
578 /// let result = Ordering::Less.then(Ordering::Equal);
579 /// assert_eq!(result, Ordering::Less);
580 ///
581 /// let result = Ordering::Less.then(Ordering::Greater);
582 /// assert_eq!(result, Ordering::Less);
583 ///
584 /// let result = Ordering::Equal.then(Ordering::Equal);
585 /// assert_eq!(result, Ordering::Equal);
586 ///
587 /// let x: (i64, i64, i64) = (1, 2, 7);
588 /// let y: (i64, i64, i64) = (1, 5, 3);
589 /// let result = x.0.cmp(&y.0).then(x.1.cmp(&y.1)).then(x.2.cmp(&y.2));
590 ///
591 /// assert_eq!(result, Ordering::Less);
592 /// ```
593 #[inline]
594 #[must_use]
595 #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")]
596 #[stable(feature = "ordering_chaining", since = "1.17.0")]
597 pub const fn then(self, other: Ordering) -> Ordering {
598 match self {
599 Equal => other,
600 _ => self,
601 }
602 }
603
604 /// Chains the ordering with the given function.
605 ///
606 /// Returns `self` when it's not `Equal`. Otherwise calls `f` and returns
607 /// the result.
608 ///
609 /// # Examples
610 ///
611 /// ```
612 /// use std::cmp::Ordering;
613 ///
614 /// let result = Ordering::Equal.then_with(|| Ordering::Less);
615 /// assert_eq!(result, Ordering::Less);
616 ///
617 /// let result = Ordering::Less.then_with(|| Ordering::Equal);
618 /// assert_eq!(result, Ordering::Less);
619 ///
620 /// let result = Ordering::Less.then_with(|| Ordering::Greater);
621 /// assert_eq!(result, Ordering::Less);
622 ///
623 /// let result = Ordering::Equal.then_with(|| Ordering::Equal);
624 /// assert_eq!(result, Ordering::Equal);
625 ///
626 /// let x: (i64, i64, i64) = (1, 2, 7);
627 /// let y: (i64, i64, i64) = (1, 5, 3);
628 /// let result = x.0.cmp(&y.0).then_with(|| x.1.cmp(&y.1)).then_with(|| x.2.cmp(&y.2));
629 ///
630 /// assert_eq!(result, Ordering::Less);
631 /// ```
632 #[inline]
633 #[must_use]
634 #[stable(feature = "ordering_chaining", since = "1.17.0")]
635 pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering {
636 match self {
637 Equal => f(),
638 _ => self,
639 }
640 }
641}
642
643/// A helper struct for reverse ordering.
644///
645/// This struct is a helper to be used with functions like [`Vec::sort_by_key`] and
646/// can be used to reverse order a part of a key.
647///
648/// [`Vec::sort_by_key`]: ../../std/vec/struct.Vec.html#method.sort_by_key
649///
650/// # Examples
651///
652/// ```
653/// use std::cmp::Reverse;
654///
655/// let mut v = vec![1, 2, 3, 4, 5, 6];
656/// v.sort_by_key(|&num| (num > 3, Reverse(num)));
657/// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]);
658/// ```
659#[derive(PartialEq, Eq, Debug, Copy, Default, Hash)]
660#[stable(feature = "reverse_cmp_key", since = "1.19.0")]
661#[repr(transparent)]
662pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T);
663
664#[stable(feature = "reverse_cmp_key", since = "1.19.0")]
665impl<T: PartialOrd> PartialOrd for Reverse<T> {
666 #[inline]
667 fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
668 other.0.partial_cmp(&self.0)
669 }
670
671 #[inline]
672 fn lt(&self, other: &Self) -> bool {
673 other.0 < self.0
674 }
675 #[inline]
676 fn le(&self, other: &Self) -> bool {
677 other.0 <= self.0
678 }
679 #[inline]
680 fn gt(&self, other: &Self) -> bool {
681 other.0 > self.0
682 }
683 #[inline]
684 fn ge(&self, other: &Self) -> bool {
685 other.0 >= self.0
686 }
687}
688
689#[stable(feature = "reverse_cmp_key", since = "1.19.0")]
690impl<T: Ord> Ord for Reverse<T> {
691 #[inline]
692 fn cmp(&self, other: &Reverse<T>) -> Ordering {
693 other.0.cmp(&self.0)
694 }
695}
696
697#[stable(feature = "reverse_cmp_key", since = "1.19.0")]
698impl<T: Clone> Clone for Reverse<T> {
699 #[inline]
700 fn clone(&self) -> Reverse<T> {
701 Reverse(self.0.clone())
702 }
703
704 #[inline]
705 fn clone_from(&mut self, source: &Self) {
706 self.0.clone_from(&source.0)
707 }
708}
709
710/// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order).
711///
712/// Implementations must be consistent with the [`PartialOrd`] implementation, and ensure `max`,
713/// `min`, and `clamp` are consistent with `cmp`:
714///
715/// - `partial_cmp(a, b) == Some(cmp(a, b))`.
716/// - `max(a, b) == max_by(a, b, cmp)` (ensured by the default implementation).
717/// - `min(a, b) == min_by(a, b, cmp)` (ensured by the default implementation).
718/// - For `a.clamp(min, max)`, see the [method docs](#method.clamp) (ensured by the default
719/// implementation).
720///
721/// Violating these requirements is a logic error. The behavior resulting from a logic error is not
722/// specified, but users of the trait must ensure that such logic errors do *not* result in
723/// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these
724/// methods.
725///
726/// ## Corollaries
727///
728/// From the above and the requirements of `PartialOrd`, it follows that for all `a`, `b` and `c`:
729///
730/// - exactly one of `a < b`, `a == b` or `a > b` is true; and
731/// - `<` is transitive: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and
732/// `>`.
733///
734/// Mathematically speaking, the `<` operator defines a strict [weak order]. In cases where `==`
735/// conforms to mathematical equality, it also defines a strict [total order].
736///
737/// [weak order]: https://en.wikipedia.org/wiki/Weak_ordering
738/// [total order]: https://en.wikipedia.org/wiki/Total_order
739///
740/// ## Derivable
741///
742/// This trait can be used with `#[derive]`.
743///
744/// When `derive`d on structs, it will produce a
745/// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering based on the
746/// top-to-bottom declaration order of the struct's members.
747///
748/// When `derive`d on enums, variants are ordered primarily by their discriminants. Secondarily,
749/// they are ordered by their fields. By default, the discriminant is smallest for variants at the
750/// top, and largest for variants at the bottom. Here's an example:
751///
752/// ```
753/// #[derive(PartialEq, Eq, PartialOrd, Ord)]
754/// enum E {
755/// Top,
756/// Bottom,
757/// }
758///
759/// assert!(E::Top < E::Bottom);
760/// ```
761///
762/// However, manually setting the discriminants can override this default behavior:
763///
764/// ```
765/// #[derive(PartialEq, Eq, PartialOrd, Ord)]
766/// enum E {
767/// Top = 2,
768/// Bottom = 1,
769/// }
770///
771/// assert!(E::Bottom < E::Top);
772/// ```
773///
774/// ## Lexicographical comparison
775///
776/// Lexicographical comparison is an operation with the following properties:
777/// - Two sequences are compared element by element.
778/// - The first mismatching element defines which sequence is lexicographically less or greater
779/// than the other.
780/// - If one sequence is a prefix of another, the shorter sequence is lexicographically less than
781/// the other.
782/// - If two sequences have equivalent elements and are of the same length, then the sequences are
783/// lexicographically equal.
784/// - An empty sequence is lexicographically less than any non-empty sequence.
785/// - Two empty sequences are lexicographically equal.
786///
787/// ## How can I implement `Ord`?
788///
789/// `Ord` requires that the type also be [`PartialOrd`], [`PartialEq`], and [`Eq`].
790///
791/// Because `Ord` implies a stronger ordering relationship than [`PartialOrd`], and both `Ord` and
792/// [`PartialOrd`] must agree, you must choose how to implement `Ord` **first**. You can choose to
793/// derive it, or implement it manually. If you derive it, you should derive all four traits. If you
794/// implement it manually, you should manually implement all four traits, based on the
795/// implementation of `Ord`.
796///
797/// Here's an example where you want to define the `Character` comparison by `health` and
798/// `experience` only, disregarding the field `mana`:
799///
800/// ```
801/// use std::cmp::Ordering;
802///
803/// struct Character {
804/// health: u32,
805/// experience: u32,
806/// mana: f32,
807/// }
808///
809/// impl Ord for Character {
810/// fn cmp(&self, other: &Self) -> Ordering {
811/// self.experience
812/// .cmp(&other.experience)
813/// .then(self.health.cmp(&other.health))
814/// }
815/// }
816///
817/// impl PartialOrd for Character {
818/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
819/// Some(self.cmp(other))
820/// }
821/// }
822///
823/// impl PartialEq for Character {
824/// fn eq(&self, other: &Self) -> bool {
825/// self.health == other.health && self.experience == other.experience
826/// }
827/// }
828///
829/// impl Eq for Character {}
830/// ```
831///
832/// If all you need is to `slice::sort` a type by a field value, it can be simpler to use
833/// `slice::sort_by_key`.
834///
835/// ## Examples of incorrect `Ord` implementations
836///
837/// ```
838/// use std::cmp::Ordering;
839///
840/// #[derive(Debug)]
841/// struct Character {
842/// health: f32,
843/// }
844///
845/// impl Ord for Character {
846/// fn cmp(&self, other: &Self) -> std::cmp::Ordering {
847/// if self.health < other.health {
848/// Ordering::Less
849/// } else if self.health > other.health {
850/// Ordering::Greater
851/// } else {
852/// Ordering::Equal
853/// }
854/// }
855/// }
856///
857/// impl PartialOrd for Character {
858/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
859/// Some(self.cmp(other))
860/// }
861/// }
862///
863/// impl PartialEq for Character {
864/// fn eq(&self, other: &Self) -> bool {
865/// self.health == other.health
866/// }
867/// }
868///
869/// impl Eq for Character {}
870///
871/// let a = Character { health: 4.5 };
872/// let b = Character { health: f32::NAN };
873///
874/// // Mistake: floating-point values do not form a total order and using the built-in comparison
875/// // operands to implement `Ord` irregardless of that reality does not change it. Use
876/// // `f32::total_cmp` if you need a total order for floating-point values.
877///
878/// // Reflexivity requirement of `Ord` is not given.
879/// assert!(a == a);
880/// assert!(b != b);
881///
882/// // Antisymmetry requirement of `Ord` is not given. Only one of a < c and c < a is allowed to be
883/// // true, not both or neither.
884/// assert_eq!((a < b) as u8 + (b < a) as u8, 0);
885/// ```
886///
887/// ```
888/// use std::cmp::Ordering;
889///
890/// #[derive(Debug)]
891/// struct Character {
892/// health: u32,
893/// experience: u32,
894/// }
895///
896/// impl PartialOrd for Character {
897/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
898/// Some(self.cmp(other))
899/// }
900/// }
901///
902/// impl Ord for Character {
903/// fn cmp(&self, other: &Self) -> std::cmp::Ordering {
904/// if self.health < 50 {
905/// self.health.cmp(&other.health)
906/// } else {
907/// self.experience.cmp(&other.experience)
908/// }
909/// }
910/// }
911///
912/// // For performance reasons implementing `PartialEq` this way is not the idiomatic way, but it
913/// // ensures consistent behavior between `PartialEq`, `PartialOrd` and `Ord` in this example.
914/// impl PartialEq for Character {
915/// fn eq(&self, other: &Self) -> bool {
916/// self.cmp(other) == Ordering::Equal
917/// }
918/// }
919///
920/// impl Eq for Character {}
921///
922/// let a = Character {
923/// health: 3,
924/// experience: 5,
925/// };
926/// let b = Character {
927/// health: 10,
928/// experience: 77,
929/// };
930/// let c = Character {
931/// health: 143,
932/// experience: 2,
933/// };
934///
935/// // Mistake: The implementation of `Ord` compares different fields depending on the value of
936/// // `self.health`, the resulting order is not total.
937///
938/// // Transitivity requirement of `Ord` is not given. If a is smaller than b and b is smaller than
939/// // c, by transitive property a must also be smaller than c.
940/// assert!(a < b && b < c && c < a);
941///
942/// // Antisymmetry requirement of `Ord` is not given. Only one of a < c and c < a is allowed to be
943/// // true, not both or neither.
944/// assert_eq!((a < c) as u8 + (c < a) as u8, 2);
945/// ```
946///
947/// The documentation of [`PartialOrd`] contains further examples, for example it's wrong for
948/// [`PartialOrd`] and [`PartialEq`] to disagree.
949///
950/// [`cmp`]: Ord::cmp
951#[doc(alias = "<")]
952#[doc(alias = ">")]
953#[doc(alias = "<=")]
954#[doc(alias = ">=")]
955#[stable(feature = "rust1", since = "1.0.0")]
956#[rustc_diagnostic_item = "Ord"]
957pub trait Ord: Eq + PartialOrd<Self> {
958 /// This method returns an [`Ordering`] between `self` and `other`.
959 ///
960 /// By convention, `self.cmp(&other)` returns the ordering matching the expression
961 /// `self <operator> other` if true.
962 ///
963 /// # Examples
964 ///
965 /// ```
966 /// use std::cmp::Ordering;
967 ///
968 /// assert_eq!(5.cmp(&10), Ordering::Less);
969 /// assert_eq!(10.cmp(&5), Ordering::Greater);
970 /// assert_eq!(5.cmp(&5), Ordering::Equal);
971 /// ```
972 #[must_use]
973 #[stable(feature = "rust1", since = "1.0.0")]
974 #[rustc_diagnostic_item = "ord_cmp_method"]
975 fn cmp(&self, other: &Self) -> Ordering;
976
977 /// Compares and returns the maximum of two values.
978 ///
979 /// Returns the second argument if the comparison determines them to be equal.
980 ///
981 /// # Examples
982 ///
983 /// ```
984 /// assert_eq!(1.max(2), 2);
985 /// assert_eq!(2.max(2), 2);
986 /// ```
987 /// ```
988 /// use std::cmp::Ordering;
989 ///
990 /// #[derive(Eq)]
991 /// struct Equal(&'static str);
992 ///
993 /// impl PartialEq for Equal {
994 /// fn eq(&self, other: &Self) -> bool { true }
995 /// }
996 /// impl PartialOrd for Equal {
997 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
998 /// }
999 /// impl Ord for Equal {
1000 /// fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
1001 /// }
1002 ///
1003 /// assert_eq!(Equal("self").max(Equal("other")).0, "other");
1004 /// ```
1005 #[stable(feature = "ord_max_min", since = "1.21.0")]
1006 #[inline]
1007 #[must_use]
1008 #[rustc_diagnostic_item = "cmp_ord_max"]
1009 fn max(self, other: Self) -> Self
1010 where
1011 Self: Sized,
1012 {
1013 if other < self { self } else { other }
1014 }
1015
1016 /// Compares and returns the minimum of two values.
1017 ///
1018 /// Returns the first argument if the comparison determines them to be equal.
1019 ///
1020 /// # Examples
1021 ///
1022 /// ```
1023 /// assert_eq!(1.min(2), 1);
1024 /// assert_eq!(2.min(2), 2);
1025 /// ```
1026 /// ```
1027 /// use std::cmp::Ordering;
1028 ///
1029 /// #[derive(Eq)]
1030 /// struct Equal(&'static str);
1031 ///
1032 /// impl PartialEq for Equal {
1033 /// fn eq(&self, other: &Self) -> bool { true }
1034 /// }
1035 /// impl PartialOrd for Equal {
1036 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
1037 /// }
1038 /// impl Ord for Equal {
1039 /// fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
1040 /// }
1041 ///
1042 /// assert_eq!(Equal("self").min(Equal("other")).0, "self");
1043 /// ```
1044 #[stable(feature = "ord_max_min", since = "1.21.0")]
1045 #[inline]
1046 #[must_use]
1047 #[rustc_diagnostic_item = "cmp_ord_min"]
1048 fn min(self, other: Self) -> Self
1049 where
1050 Self: Sized,
1051 {
1052 if other < self { other } else { self }
1053 }
1054
1055 /// Restrict a value to a certain interval.
1056 ///
1057 /// Returns `max` if `self` is greater than `max`, and `min` if `self` is
1058 /// less than `min`. Otherwise this returns `self`.
1059 ///
1060 /// # Panics
1061 ///
1062 /// Panics if `min > max`.
1063 ///
1064 /// # Examples
1065 ///
1066 /// ```
1067 /// assert_eq!((-3).clamp(-2, 1), -2);
1068 /// assert_eq!(0.clamp(-2, 1), 0);
1069 /// assert_eq!(2.clamp(-2, 1), 1);
1070 /// ```
1071 #[must_use]
1072 #[inline]
1073 #[stable(feature = "clamp", since = "1.50.0")]
1074 fn clamp(self, min: Self, max: Self) -> Self
1075 where
1076 Self: Sized,
1077 {
1078 assert!(min <= max);
1079 if self < min {
1080 min
1081 } else if self > max {
1082 max
1083 } else {
1084 self
1085 }
1086 }
1087}
1088
1089/// Derive macro generating an impl of the trait [`Ord`].
1090/// The behavior of this macro is described in detail [here](Ord#derivable).
1091#[rustc_builtin_macro]
1092#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
1093#[allow_internal_unstable(core_intrinsics)]
1094pub macro Ord($item:item) {
1095 /* compiler built-in */
1096}
1097
1098/// Trait for types that form a [partial order](https://en.wikipedia.org/wiki/Partial_order).
1099///
1100/// The `lt`, `le`, `gt`, and `ge` methods of this trait can be called using the `<`, `<=`, `>`, and
1101/// `>=` operators, respectively.
1102///
1103/// This trait should **only** contain the comparison logic for a type **if one plans on only
1104/// implementing `PartialOrd` but not [`Ord`]**. Otherwise the comparison logic should be in [`Ord`]
1105/// and this trait implemented with `Some(self.cmp(other))`.
1106///
1107/// The methods of this trait must be consistent with each other and with those of [`PartialEq`].
1108/// The following conditions must hold:
1109///
1110/// 1. `a == b` if and only if `partial_cmp(a, b) == Some(Equal)`.
1111/// 2. `a < b` if and only if `partial_cmp(a, b) == Some(Less)`
1112/// 3. `a > b` if and only if `partial_cmp(a, b) == Some(Greater)`
1113/// 4. `a <= b` if and only if `a < b || a == b`
1114/// 5. `a >= b` if and only if `a > b || a == b`
1115/// 6. `a != b` if and only if `!(a == b)`.
1116///
1117/// Conditions 2–5 above are ensured by the default implementation. Condition 6 is already ensured
1118/// by [`PartialEq`].
1119///
1120/// If [`Ord`] is also implemented for `Self` and `Rhs`, it must also be consistent with
1121/// `partial_cmp` (see the documentation of that trait for the exact requirements). It's easy to
1122/// accidentally make them disagree by deriving some of the traits and manually implementing others.
1123///
1124/// The comparison relations must satisfy the following conditions (for all `a`, `b`, `c` of type
1125/// `A`, `B`, `C`):
1126///
1127/// - **Transitivity**: if `A: PartialOrd<B>` and `B: PartialOrd<C>` and `A: PartialOrd<C>`, then `a
1128/// < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. This must also
1129/// work for longer chains, such as when `A: PartialOrd<B>`, `B: PartialOrd<C>`, `C:
1130/// PartialOrd<D>`, and `A: PartialOrd<D>` all exist.
1131/// - **Duality**: if `A: PartialOrd<B>` and `B: PartialOrd<A>`, then `a < b` if and only if `b >
1132/// a`.
1133///
1134/// Note that the `B: PartialOrd<A>` (dual) and `A: PartialOrd<C>` (transitive) impls are not forced
1135/// to exist, but these requirements apply whenever they do exist.
1136///
1137/// Violating these requirements is a logic error. The behavior resulting from a logic error is not
1138/// specified, but users of the trait must ensure that such logic errors do *not* result in
1139/// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these
1140/// methods.
1141///
1142/// ## Cross-crate considerations
1143///
1144/// Upholding the requirements stated above can become tricky when one crate implements `PartialOrd`
1145/// for a type of another crate (i.e., to allow comparing one of its own types with a type from the
1146/// standard library). The recommendation is to never implement this trait for a foreign type. In
1147/// other words, such a crate should do `impl PartialOrd<ForeignType> for LocalType`, but it should
1148/// *not* do `impl PartialOrd<LocalType> for ForeignType`.
1149///
1150/// This avoids the problem of transitive chains that criss-cross crate boundaries: for all local
1151/// types `T`, you may assume that no other crate will add `impl`s that allow comparing `T < U`. In
1152/// other words, if other crates add `impl`s that allow building longer transitive chains `U1 < ...
1153/// < T < V1 < ...`, then all the types that appear to the right of `T` must be types that the crate
1154/// defining `T` already knows about. This rules out transitive chains where downstream crates can
1155/// add new `impl`s that "stitch together" comparisons of foreign types in ways that violate
1156/// transitivity.
1157///
1158/// Not having such foreign `impl`s also avoids forward compatibility issues where one crate adding
1159/// more `PartialOrd` implementations can cause build failures in downstream crates.
1160///
1161/// ## Corollaries
1162///
1163/// The following corollaries follow from the above requirements:
1164///
1165/// - irreflexivity of `<` and `>`: `!(a < a)`, `!(a > a)`
1166/// - transitivity of `>`: if `a > b` and `b > c` then `a > c`
1167/// - duality of `partial_cmp`: `partial_cmp(a, b) == partial_cmp(b, a).map(Ordering::reverse)`
1168///
1169/// ## Strict and non-strict partial orders
1170///
1171/// The `<` and `>` operators behave according to a *strict* partial order. However, `<=` and `>=`
1172/// do **not** behave according to a *non-strict* partial order. That is because mathematically, a
1173/// non-strict partial order would require reflexivity, i.e. `a <= a` would need to be true for
1174/// every `a`. This isn't always the case for types that implement `PartialOrd`, for example:
1175///
1176/// ```
1177/// let a = f64::sqrt(-1.0);
1178/// assert_eq!(a <= a, false);
1179/// ```
1180///
1181/// ## Derivable
1182///
1183/// This trait can be used with `#[derive]`.
1184///
1185/// When `derive`d on structs, it will produce a
1186/// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering based on the
1187/// top-to-bottom declaration order of the struct's members.
1188///
1189/// When `derive`d on enums, variants are primarily ordered by their discriminants. Secondarily,
1190/// they are ordered by their fields. By default, the discriminant is smallest for variants at the
1191/// top, and largest for variants at the bottom. Here's an example:
1192///
1193/// ```
1194/// #[derive(PartialEq, PartialOrd)]
1195/// enum E {
1196/// Top,
1197/// Bottom,
1198/// }
1199///
1200/// assert!(E::Top < E::Bottom);
1201/// ```
1202///
1203/// However, manually setting the discriminants can override this default behavior:
1204///
1205/// ```
1206/// #[derive(PartialEq, PartialOrd)]
1207/// enum E {
1208/// Top = 2,
1209/// Bottom = 1,
1210/// }
1211///
1212/// assert!(E::Bottom < E::Top);
1213/// ```
1214///
1215/// ## How can I implement `PartialOrd`?
1216///
1217/// `PartialOrd` only requires implementation of the [`partial_cmp`] method, with the others
1218/// generated from default implementations.
1219///
1220/// However it remains possible to implement the others separately for types which do not have a
1221/// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 == false`
1222/// (cf. IEEE 754-2008 section 5.11).
1223///
1224/// `PartialOrd` requires your type to be [`PartialEq`].
1225///
1226/// If your type is [`Ord`], you can implement [`partial_cmp`] by using [`cmp`]:
1227///
1228/// ```
1229/// use std::cmp::Ordering;
1230///
1231/// struct Person {
1232/// id: u32,
1233/// name: String,
1234/// height: u32,
1235/// }
1236///
1237/// impl PartialOrd for Person {
1238/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1239/// Some(self.cmp(other))
1240/// }
1241/// }
1242///
1243/// impl Ord for Person {
1244/// fn cmp(&self, other: &Self) -> Ordering {
1245/// self.height.cmp(&other.height)
1246/// }
1247/// }
1248///
1249/// impl PartialEq for Person {
1250/// fn eq(&self, other: &Self) -> bool {
1251/// self.height == other.height
1252/// }
1253/// }
1254///
1255/// impl Eq for Person {}
1256/// ```
1257///
1258/// You may also find it useful to use [`partial_cmp`] on your type's fields. Here is an example of
1259/// `Person` types who have a floating-point `height` field that is the only field to be used for
1260/// sorting:
1261///
1262/// ```
1263/// use std::cmp::Ordering;
1264///
1265/// struct Person {
1266/// id: u32,
1267/// name: String,
1268/// height: f64,
1269/// }
1270///
1271/// impl PartialOrd for Person {
1272/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1273/// self.height.partial_cmp(&other.height)
1274/// }
1275/// }
1276///
1277/// impl PartialEq for Person {
1278/// fn eq(&self, other: &Self) -> bool {
1279/// self.height == other.height
1280/// }
1281/// }
1282/// ```
1283///
1284/// ## Examples of incorrect `PartialOrd` implementations
1285///
1286/// ```
1287/// use std::cmp::Ordering;
1288///
1289/// #[derive(PartialEq, Debug)]
1290/// struct Character {
1291/// health: u32,
1292/// experience: u32,
1293/// }
1294///
1295/// impl PartialOrd for Character {
1296/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1297/// Some(self.health.cmp(&other.health))
1298/// }
1299/// }
1300///
1301/// let a = Character {
1302/// health: 10,
1303/// experience: 5,
1304/// };
1305/// let b = Character {
1306/// health: 10,
1307/// experience: 77,
1308/// };
1309///
1310/// // Mistake: `PartialEq` and `PartialOrd` disagree with each other.
1311///
1312/// assert_eq!(a.partial_cmp(&b).unwrap(), Ordering::Equal); // a == b according to `PartialOrd`.
1313/// assert_ne!(a, b); // a != b according to `PartialEq`.
1314/// ```
1315///
1316/// # Examples
1317///
1318/// ```
1319/// let x: u32 = 0;
1320/// let y: u32 = 1;
1321///
1322/// assert_eq!(x < y, true);
1323/// assert_eq!(x.lt(&y), true);
1324/// ```
1325///
1326/// [`partial_cmp`]: PartialOrd::partial_cmp
1327/// [`cmp`]: Ord::cmp
1328#[lang = "partial_ord"]
1329#[stable(feature = "rust1", since = "1.0.0")]
1330#[doc(alias = ">")]
1331#[doc(alias = "<")]
1332#[doc(alias = "<=")]
1333#[doc(alias = ">=")]
1334#[rustc_on_unimplemented(
1335 message = "can't compare `{Self}` with `{Rhs}`",
1336 label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`",
1337 append_const_msg
1338)]
1339#[rustc_diagnostic_item = "PartialOrd"]
1340pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
1341 /// This method returns an ordering between `self` and `other` values if one exists.
1342 ///
1343 /// # Examples
1344 ///
1345 /// ```
1346 /// use std::cmp::Ordering;
1347 ///
1348 /// let result = 1.0.partial_cmp(&2.0);
1349 /// assert_eq!(result, Some(Ordering::Less));
1350 ///
1351 /// let result = 1.0.partial_cmp(&1.0);
1352 /// assert_eq!(result, Some(Ordering::Equal));
1353 ///
1354 /// let result = 2.0.partial_cmp(&1.0);
1355 /// assert_eq!(result, Some(Ordering::Greater));
1356 /// ```
1357 ///
1358 /// When comparison is impossible:
1359 ///
1360 /// ```
1361 /// let result = f64::NAN.partial_cmp(&1.0);
1362 /// assert_eq!(result, None);
1363 /// ```
1364 #[must_use]
1365 #[stable(feature = "rust1", since = "1.0.0")]
1366 #[rustc_diagnostic_item = "cmp_partialord_cmp"]
1367 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
1368
1369 /// Tests less than (for `self` and `other`) and is used by the `<` operator.
1370 ///
1371 /// # Examples
1372 ///
1373 /// ```
1374 /// assert_eq!(1.0 < 1.0, false);
1375 /// assert_eq!(1.0 < 2.0, true);
1376 /// assert_eq!(2.0 < 1.0, false);
1377 /// ```
1378 #[inline]
1379 #[must_use]
1380 #[stable(feature = "rust1", since = "1.0.0")]
1381 #[rustc_diagnostic_item = "cmp_partialord_lt"]
1382 fn lt(&self, other: &Rhs) -> bool {
1383 self.partial_cmp(other).is_some_and(Ordering::is_lt)
1384 }
1385
1386 /// Tests less than or equal to (for `self` and `other`) and is used by the
1387 /// `<=` operator.
1388 ///
1389 /// # Examples
1390 ///
1391 /// ```
1392 /// assert_eq!(1.0 <= 1.0, true);
1393 /// assert_eq!(1.0 <= 2.0, true);
1394 /// assert_eq!(2.0 <= 1.0, false);
1395 /// ```
1396 #[inline]
1397 #[must_use]
1398 #[stable(feature = "rust1", since = "1.0.0")]
1399 #[rustc_diagnostic_item = "cmp_partialord_le"]
1400 fn le(&self, other: &Rhs) -> bool {
1401 self.partial_cmp(other).is_some_and(Ordering::is_le)
1402 }
1403
1404 /// Tests greater than (for `self` and `other`) and is used by the `>`
1405 /// operator.
1406 ///
1407 /// # Examples
1408 ///
1409 /// ```
1410 /// assert_eq!(1.0 > 1.0, false);
1411 /// assert_eq!(1.0 > 2.0, false);
1412 /// assert_eq!(2.0 > 1.0, true);
1413 /// ```
1414 #[inline]
1415 #[must_use]
1416 #[stable(feature = "rust1", since = "1.0.0")]
1417 #[rustc_diagnostic_item = "cmp_partialord_gt"]
1418 fn gt(&self, other: &Rhs) -> bool {
1419 self.partial_cmp(other).is_some_and(Ordering::is_gt)
1420 }
1421
1422 /// Tests greater than or equal to (for `self` and `other`) and is used by
1423 /// the `>=` operator.
1424 ///
1425 /// # Examples
1426 ///
1427 /// ```
1428 /// assert_eq!(1.0 >= 1.0, true);
1429 /// assert_eq!(1.0 >= 2.0, false);
1430 /// assert_eq!(2.0 >= 1.0, true);
1431 /// ```
1432 #[inline]
1433 #[must_use]
1434 #[stable(feature = "rust1", since = "1.0.0")]
1435 #[rustc_diagnostic_item = "cmp_partialord_ge"]
1436 fn ge(&self, other: &Rhs) -> bool {
1437 self.partial_cmp(other).is_some_and(Ordering::is_ge)
1438 }
1439
1440 /// If `self == other`, returns `ControlFlow::Continue(())`.
1441 /// Otherwise, returns `ControlFlow::Break(self < other)`.
1442 ///
1443 /// This is useful for chaining together calls when implementing a lexical
1444 /// `PartialOrd::lt`, as it allows types (like primitives) which can cheaply
1445 /// check `==` and `<` separately to do rather than needing to calculate
1446 /// (then optimize out) the three-way `Ordering` result.
1447 #[inline]
1448 #[must_use]
1449 // Added to improve the behaviour of tuples; not necessarily stabilization-track.
1450 #[unstable(feature = "partial_ord_chaining_methods", issue = "none")]
1451 #[doc(hidden)]
1452 fn __chaining_lt(&self, other: &Rhs) -> ControlFlow<bool> {
1453 default_chaining_impl(self, other, Ordering::is_lt)
1454 }
1455
1456 /// Same as `__chaining_lt`, but for `<=` instead of `<`.
1457 #[inline]
1458 #[must_use]
1459 #[unstable(feature = "partial_ord_chaining_methods", issue = "none")]
1460 #[doc(hidden)]
1461 fn __chaining_le(&self, other: &Rhs) -> ControlFlow<bool> {
1462 default_chaining_impl(self, other, Ordering::is_le)
1463 }
1464
1465 /// Same as `__chaining_lt`, but for `>` instead of `<`.
1466 #[inline]
1467 #[must_use]
1468 #[unstable(feature = "partial_ord_chaining_methods", issue = "none")]
1469 #[doc(hidden)]
1470 fn __chaining_gt(&self, other: &Rhs) -> ControlFlow<bool> {
1471 default_chaining_impl(self, other, Ordering::is_gt)
1472 }
1473
1474 /// Same as `__chaining_lt`, but for `>=` instead of `<`.
1475 #[inline]
1476 #[must_use]
1477 #[unstable(feature = "partial_ord_chaining_methods", issue = "none")]
1478 #[doc(hidden)]
1479 fn __chaining_ge(&self, other: &Rhs) -> ControlFlow<bool> {
1480 default_chaining_impl(self, other, Ordering::is_ge)
1481 }
1482}
1483
1484fn default_chaining_impl<T: ?Sized, U: ?Sized>(
1485 lhs: &T,
1486 rhs: &U,
1487 p: impl FnOnce(Ordering) -> bool,
1488) -> ControlFlow<bool>
1489where
1490 T: PartialOrd<U>,
1491{
1492 // It's important that this only call `partial_cmp` once, not call `eq` then
1493 // one of the relational operators. We don't want to `bcmp`-then-`memcp` a
1494 // `String`, for example, or similarly for other data structures (#108157).
1495 match <T as PartialOrd<U>>::partial_cmp(self:lhs, other:rhs) {
1496 Some(Equal) => ControlFlow::Continue(()),
1497 Some(c: Ordering) => ControlFlow::Break(p(c)),
1498 None => ControlFlow::Break(false),
1499 }
1500}
1501
1502/// Derive macro generating an impl of the trait [`PartialOrd`].
1503/// The behavior of this macro is described in detail [here](PartialOrd#derivable).
1504#[rustc_builtin_macro]
1505#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
1506#[allow_internal_unstable(core_intrinsics)]
1507pub macro PartialOrd($item:item) {
1508 /* compiler built-in */
1509}
1510
1511/// Compares and returns the minimum of two values.
1512///
1513/// Returns the first argument if the comparison determines them to be equal.
1514///
1515/// Internally uses an alias to [`Ord::min`].
1516///
1517/// # Examples
1518///
1519/// ```
1520/// use std::cmp;
1521///
1522/// assert_eq!(cmp::min(1, 2), 1);
1523/// assert_eq!(cmp::min(2, 2), 2);
1524/// ```
1525/// ```
1526/// use std::cmp::{self, Ordering};
1527///
1528/// #[derive(Eq)]
1529/// struct Equal(&'static str);
1530///
1531/// impl PartialEq for Equal {
1532/// fn eq(&self, other: &Self) -> bool { true }
1533/// }
1534/// impl PartialOrd for Equal {
1535/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
1536/// }
1537/// impl Ord for Equal {
1538/// fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
1539/// }
1540///
1541/// assert_eq!(cmp::min(Equal("v1"), Equal("v2")).0, "v1");
1542/// ```
1543#[inline]
1544#[must_use]
1545#[stable(feature = "rust1", since = "1.0.0")]
1546#[rustc_diagnostic_item = "cmp_min"]
1547pub fn min<T: Ord>(v1: T, v2: T) -> T {
1548 v1.min(v2)
1549}
1550
1551/// Returns the minimum of two values with respect to the specified comparison function.
1552///
1553/// Returns the first argument if the comparison determines them to be equal.
1554///
1555/// # Examples
1556///
1557/// ```
1558/// use std::cmp;
1559///
1560/// let abs_cmp = |x: &i32, y: &i32| x.abs().cmp(&y.abs());
1561///
1562/// let result = cmp::min_by(2, -1, abs_cmp);
1563/// assert_eq!(result, -1);
1564///
1565/// let result = cmp::min_by(2, -3, abs_cmp);
1566/// assert_eq!(result, 2);
1567///
1568/// let result = cmp::min_by(1, -1, abs_cmp);
1569/// assert_eq!(result, 1);
1570/// ```
1571#[inline]
1572#[must_use]
1573#[stable(feature = "cmp_min_max_by", since = "1.53.0")]
1574pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
1575 if compare(&v2, &v1).is_lt() { v2 } else { v1 }
1576}
1577
1578/// Returns the element that gives the minimum value from the specified function.
1579///
1580/// Returns the first argument if the comparison determines them to be equal.
1581///
1582/// # Examples
1583///
1584/// ```
1585/// use std::cmp;
1586///
1587/// let result = cmp::min_by_key(2, -1, |x: &i32| x.abs());
1588/// assert_eq!(result, -1);
1589///
1590/// let result = cmp::min_by_key(2, -3, |x: &i32| x.abs());
1591/// assert_eq!(result, 2);
1592///
1593/// let result = cmp::min_by_key(1, -1, |x: &i32| x.abs());
1594/// assert_eq!(result, 1);
1595/// ```
1596#[inline]
1597#[must_use]
1598#[stable(feature = "cmp_min_max_by", since = "1.53.0")]
1599pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
1600 if f(&v2) < f(&v1) { v2 } else { v1 }
1601}
1602
1603/// Compares and returns the maximum of two values.
1604///
1605/// Returns the second argument if the comparison determines them to be equal.
1606///
1607/// Internally uses an alias to [`Ord::max`].
1608///
1609/// # Examples
1610///
1611/// ```
1612/// use std::cmp;
1613///
1614/// assert_eq!(cmp::max(1, 2), 2);
1615/// assert_eq!(cmp::max(2, 2), 2);
1616/// ```
1617/// ```
1618/// use std::cmp::{self, Ordering};
1619///
1620/// #[derive(Eq)]
1621/// struct Equal(&'static str);
1622///
1623/// impl PartialEq for Equal {
1624/// fn eq(&self, other: &Self) -> bool { true }
1625/// }
1626/// impl PartialOrd for Equal {
1627/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
1628/// }
1629/// impl Ord for Equal {
1630/// fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
1631/// }
1632///
1633/// assert_eq!(cmp::max(Equal("v1"), Equal("v2")).0, "v2");
1634/// ```
1635#[inline]
1636#[must_use]
1637#[stable(feature = "rust1", since = "1.0.0")]
1638#[rustc_diagnostic_item = "cmp_max"]
1639pub fn max<T: Ord>(v1: T, v2: T) -> T {
1640 v1.max(v2)
1641}
1642
1643/// Returns the maximum of two values with respect to the specified comparison function.
1644///
1645/// Returns the second argument if the comparison determines them to be equal.
1646///
1647/// # Examples
1648///
1649/// ```
1650/// use std::cmp;
1651///
1652/// let abs_cmp = |x: &i32, y: &i32| x.abs().cmp(&y.abs());
1653///
1654/// let result = cmp::max_by(3, -2, abs_cmp) ;
1655/// assert_eq!(result, 3);
1656///
1657/// let result = cmp::max_by(1, -2, abs_cmp);
1658/// assert_eq!(result, -2);
1659///
1660/// let result = cmp::max_by(1, -1, abs_cmp);
1661/// assert_eq!(result, -1);
1662/// ```
1663#[inline]
1664#[must_use]
1665#[stable(feature = "cmp_min_max_by", since = "1.53.0")]
1666pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
1667 if compare(&v2, &v1).is_lt() { v1 } else { v2 }
1668}
1669
1670/// Returns the element that gives the maximum value from the specified function.
1671///
1672/// Returns the second argument if the comparison determines them to be equal.
1673///
1674/// # Examples
1675///
1676/// ```
1677/// use std::cmp;
1678///
1679/// let result = cmp::max_by_key(3, -2, |x: &i32| x.abs());
1680/// assert_eq!(result, 3);
1681///
1682/// let result = cmp::max_by_key(1, -2, |x: &i32| x.abs());
1683/// assert_eq!(result, -2);
1684///
1685/// let result = cmp::max_by_key(1, -1, |x: &i32| x.abs());
1686/// assert_eq!(result, -1);
1687/// ```
1688#[inline]
1689#[must_use]
1690#[stable(feature = "cmp_min_max_by", since = "1.53.0")]
1691pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
1692 if f(&v2) < f(&v1) { v1 } else { v2 }
1693}
1694
1695/// Compares and sorts two values, returning minimum and maximum.
1696///
1697/// Returns `[v1, v2]` if the comparison determines them to be equal.
1698///
1699/// # Examples
1700///
1701/// ```
1702/// #![feature(cmp_minmax)]
1703/// use std::cmp;
1704///
1705/// assert_eq!(cmp::minmax(1, 2), [1, 2]);
1706/// assert_eq!(cmp::minmax(2, 1), [1, 2]);
1707///
1708/// // You can destructure the result using array patterns
1709/// let [min, max] = cmp::minmax(42, 17);
1710/// assert_eq!(min, 17);
1711/// assert_eq!(max, 42);
1712/// ```
1713/// ```
1714/// #![feature(cmp_minmax)]
1715/// use std::cmp::{self, Ordering};
1716///
1717/// #[derive(Eq)]
1718/// struct Equal(&'static str);
1719///
1720/// impl PartialEq for Equal {
1721/// fn eq(&self, other: &Self) -> bool { true }
1722/// }
1723/// impl PartialOrd for Equal {
1724/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(Ordering::Equal) }
1725/// }
1726/// impl Ord for Equal {
1727/// fn cmp(&self, other: &Self) -> Ordering { Ordering::Equal }
1728/// }
1729///
1730/// assert_eq!(cmp::minmax(Equal("v1"), Equal("v2")).map(|v| v.0), ["v1", "v2"]);
1731/// ```
1732#[inline]
1733#[must_use]
1734#[unstable(feature = "cmp_minmax", issue = "115939")]
1735pub fn minmax<T>(v1: T, v2: T) -> [T; 2]
1736where
1737 T: Ord,
1738{
1739 if v2 < v1 { [v2, v1] } else { [v1, v2] }
1740}
1741
1742/// Returns minimum and maximum values with respect to the specified comparison function.
1743///
1744/// Returns `[v1, v2]` if the comparison determines them to be equal.
1745///
1746/// # Examples
1747///
1748/// ```
1749/// #![feature(cmp_minmax)]
1750/// use std::cmp;
1751///
1752/// let abs_cmp = |x: &i32, y: &i32| x.abs().cmp(&y.abs());
1753///
1754/// assert_eq!(cmp::minmax_by(-2, 1, abs_cmp), [1, -2]);
1755/// assert_eq!(cmp::minmax_by(-1, 2, abs_cmp), [-1, 2]);
1756/// assert_eq!(cmp::minmax_by(-2, 2, abs_cmp), [-2, 2]);
1757///
1758/// // You can destructure the result using array patterns
1759/// let [min, max] = cmp::minmax_by(-42, 17, abs_cmp);
1760/// assert_eq!(min, 17);
1761/// assert_eq!(max, -42);
1762/// ```
1763#[inline]
1764#[must_use]
1765#[unstable(feature = "cmp_minmax", issue = "115939")]
1766pub fn minmax_by<T, F>(v1: T, v2: T, compare: F) -> [T; 2]
1767where
1768 F: FnOnce(&T, &T) -> Ordering,
1769{
1770 if compare(&v2, &v1).is_lt() { [v2, v1] } else { [v1, v2] }
1771}
1772
1773/// Returns minimum and maximum values with respect to the specified key function.
1774///
1775/// Returns `[v1, v2]` if the comparison determines them to be equal.
1776///
1777/// # Examples
1778///
1779/// ```
1780/// #![feature(cmp_minmax)]
1781/// use std::cmp;
1782///
1783/// assert_eq!(cmp::minmax_by_key(-2, 1, |x: &i32| x.abs()), [1, -2]);
1784/// assert_eq!(cmp::minmax_by_key(-2, 2, |x: &i32| x.abs()), [-2, 2]);
1785///
1786/// // You can destructure the result using array patterns
1787/// let [min, max] = cmp::minmax_by_key(-42, 17, |x: &i32| x.abs());
1788/// assert_eq!(min, 17);
1789/// assert_eq!(max, -42);
1790/// ```
1791#[inline]
1792#[must_use]
1793#[unstable(feature = "cmp_minmax", issue = "115939")]
1794pub fn minmax_by_key<T, F, K>(v1: T, v2: T, mut f: F) -> [T; 2]
1795where
1796 F: FnMut(&T) -> K,
1797 K: Ord,
1798{
1799 if f(&v2) < f(&v1) { [v2, v1] } else { [v1, v2] }
1800}
1801
1802// Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
1803mod impls {
1804 use crate::cmp::Ordering::{self, Equal, Greater, Less};
1805 use crate::hint::unreachable_unchecked;
1806 use crate::ops::ControlFlow::{self, Break, Continue};
1807
1808 macro_rules! partial_eq_impl {
1809 ($($t:ty)*) => ($(
1810 #[stable(feature = "rust1", since = "1.0.0")]
1811 impl PartialEq for $t {
1812 #[inline]
1813 fn eq(&self, other: &Self) -> bool { *self == *other }
1814 #[inline]
1815 fn ne(&self, other: &Self) -> bool { *self != *other }
1816 }
1817 )*)
1818 }
1819
1820 #[stable(feature = "rust1", since = "1.0.0")]
1821 impl PartialEq for () {
1822 #[inline]
1823 fn eq(&self, _other: &()) -> bool {
1824 true
1825 }
1826 #[inline]
1827 fn ne(&self, _other: &()) -> bool {
1828 false
1829 }
1830 }
1831
1832 partial_eq_impl! {
1833 bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f16 f32 f64 f128
1834 }
1835
1836 macro_rules! eq_impl {
1837 ($($t:ty)*) => ($(
1838 #[stable(feature = "rust1", since = "1.0.0")]
1839 impl Eq for $t {}
1840 )*)
1841 }
1842
1843 eq_impl! { () bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1844
1845 #[rustfmt::skip]
1846 macro_rules! partial_ord_methods_primitive_impl {
1847 () => {
1848 #[inline(always)]
1849 fn lt(&self, other: &Self) -> bool { *self < *other }
1850 #[inline(always)]
1851 fn le(&self, other: &Self) -> bool { *self <= *other }
1852 #[inline(always)]
1853 fn gt(&self, other: &Self) -> bool { *self > *other }
1854 #[inline(always)]
1855 fn ge(&self, other: &Self) -> bool { *self >= *other }
1856
1857 // These implementations are the same for `Ord` or `PartialOrd` types
1858 // because if either is NAN the `==` test will fail so we end up in
1859 // the `Break` case and the comparison will correctly return `false`.
1860
1861 #[inline]
1862 fn __chaining_lt(&self, other: &Self) -> ControlFlow<bool> {
1863 let (lhs, rhs) = (*self, *other);
1864 if lhs == rhs { Continue(()) } else { Break(lhs < rhs) }
1865 }
1866 #[inline]
1867 fn __chaining_le(&self, other: &Self) -> ControlFlow<bool> {
1868 let (lhs, rhs) = (*self, *other);
1869 if lhs == rhs { Continue(()) } else { Break(lhs <= rhs) }
1870 }
1871 #[inline]
1872 fn __chaining_gt(&self, other: &Self) -> ControlFlow<bool> {
1873 let (lhs, rhs) = (*self, *other);
1874 if lhs == rhs { Continue(()) } else { Break(lhs > rhs) }
1875 }
1876 #[inline]
1877 fn __chaining_ge(&self, other: &Self) -> ControlFlow<bool> {
1878 let (lhs, rhs) = (*self, *other);
1879 if lhs == rhs { Continue(()) } else { Break(lhs >= rhs) }
1880 }
1881 };
1882 }
1883
1884 macro_rules! partial_ord_impl {
1885 ($($t:ty)*) => ($(
1886 #[stable(feature = "rust1", since = "1.0.0")]
1887 impl PartialOrd for $t {
1888 #[inline]
1889 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1890 match (*self <= *other, *self >= *other) {
1891 (false, false) => None,
1892 (false, true) => Some(Greater),
1893 (true, false) => Some(Less),
1894 (true, true) => Some(Equal),
1895 }
1896 }
1897
1898 partial_ord_methods_primitive_impl!();
1899 }
1900 )*)
1901 }
1902
1903 #[stable(feature = "rust1", since = "1.0.0")]
1904 impl PartialOrd for () {
1905 #[inline]
1906 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
1907 Some(Equal)
1908 }
1909 }
1910
1911 #[stable(feature = "rust1", since = "1.0.0")]
1912 impl PartialOrd for bool {
1913 #[inline]
1914 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
1915 Some(self.cmp(other))
1916 }
1917
1918 partial_ord_methods_primitive_impl!();
1919 }
1920
1921 partial_ord_impl! { f16 f32 f64 f128 }
1922
1923 macro_rules! ord_impl {
1924 ($($t:ty)*) => ($(
1925 #[stable(feature = "rust1", since = "1.0.0")]
1926 impl PartialOrd for $t {
1927 #[inline]
1928 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1929 Some(crate::intrinsics::three_way_compare(*self, *other))
1930 }
1931
1932 partial_ord_methods_primitive_impl!();
1933 }
1934
1935 #[stable(feature = "rust1", since = "1.0.0")]
1936 impl Ord for $t {
1937 #[inline]
1938 fn cmp(&self, other: &Self) -> Ordering {
1939 crate::intrinsics::three_way_compare(*self, *other)
1940 }
1941 }
1942 )*)
1943 }
1944
1945 #[stable(feature = "rust1", since = "1.0.0")]
1946 impl Ord for () {
1947 #[inline]
1948 fn cmp(&self, _other: &()) -> Ordering {
1949 Equal
1950 }
1951 }
1952
1953 #[stable(feature = "rust1", since = "1.0.0")]
1954 impl Ord for bool {
1955 #[inline]
1956 fn cmp(&self, other: &bool) -> Ordering {
1957 // Casting to i8's and converting the difference to an Ordering generates
1958 // more optimal assembly.
1959 // See <https://github.com/rust-lang/rust/issues/66780> for more info.
1960 match (*self as i8) - (*other as i8) {
1961 -1 => Less,
1962 0 => Equal,
1963 1 => Greater,
1964 // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else
1965 _ => unsafe { unreachable_unchecked() },
1966 }
1967 }
1968
1969 #[inline]
1970 fn min(self, other: bool) -> bool {
1971 self & other
1972 }
1973
1974 #[inline]
1975 fn max(self, other: bool) -> bool {
1976 self | other
1977 }
1978
1979 #[inline]
1980 fn clamp(self, min: bool, max: bool) -> bool {
1981 assert!(min <= max);
1982 self.max(min).min(max)
1983 }
1984 }
1985
1986 ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1987
1988 #[unstable(feature = "never_type", issue = "35121")]
1989 impl PartialEq for ! {
1990 #[inline]
1991 fn eq(&self, _: &!) -> bool {
1992 *self
1993 }
1994 }
1995
1996 #[unstable(feature = "never_type", issue = "35121")]
1997 impl Eq for ! {}
1998
1999 #[unstable(feature = "never_type", issue = "35121")]
2000 impl PartialOrd for ! {
2001 #[inline]
2002 fn partial_cmp(&self, _: &!) -> Option<Ordering> {
2003 *self
2004 }
2005 }
2006
2007 #[unstable(feature = "never_type", issue = "35121")]
2008 impl Ord for ! {
2009 #[inline]
2010 fn cmp(&self, _: &!) -> Ordering {
2011 *self
2012 }
2013 }
2014
2015 // & pointers
2016
2017 #[stable(feature = "rust1", since = "1.0.0")]
2018 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A
2019 where
2020 A: PartialEq<B>,
2021 {
2022 #[inline]
2023 fn eq(&self, other: &&B) -> bool {
2024 PartialEq::eq(*self, *other)
2025 }
2026 #[inline]
2027 fn ne(&self, other: &&B) -> bool {
2028 PartialEq::ne(*self, *other)
2029 }
2030 }
2031 #[stable(feature = "rust1", since = "1.0.0")]
2032 impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A
2033 where
2034 A: PartialOrd<B>,
2035 {
2036 #[inline]
2037 fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
2038 PartialOrd::partial_cmp(*self, *other)
2039 }
2040 #[inline]
2041 fn lt(&self, other: &&B) -> bool {
2042 PartialOrd::lt(*self, *other)
2043 }
2044 #[inline]
2045 fn le(&self, other: &&B) -> bool {
2046 PartialOrd::le(*self, *other)
2047 }
2048 #[inline]
2049 fn gt(&self, other: &&B) -> bool {
2050 PartialOrd::gt(*self, *other)
2051 }
2052 #[inline]
2053 fn ge(&self, other: &&B) -> bool {
2054 PartialOrd::ge(*self, *other)
2055 }
2056 }
2057 #[stable(feature = "rust1", since = "1.0.0")]
2058 impl<A: ?Sized> Ord for &A
2059 where
2060 A: Ord,
2061 {
2062 #[inline]
2063 fn cmp(&self, other: &Self) -> Ordering {
2064 Ord::cmp(*self, *other)
2065 }
2066 }
2067 #[stable(feature = "rust1", since = "1.0.0")]
2068 impl<A: ?Sized> Eq for &A where A: Eq {}
2069
2070 // &mut pointers
2071
2072 #[stable(feature = "rust1", since = "1.0.0")]
2073 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A
2074 where
2075 A: PartialEq<B>,
2076 {
2077 #[inline]
2078 fn eq(&self, other: &&mut B) -> bool {
2079 PartialEq::eq(*self, *other)
2080 }
2081 #[inline]
2082 fn ne(&self, other: &&mut B) -> bool {
2083 PartialEq::ne(*self, *other)
2084 }
2085 }
2086 #[stable(feature = "rust1", since = "1.0.0")]
2087 impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A
2088 where
2089 A: PartialOrd<B>,
2090 {
2091 #[inline]
2092 fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> {
2093 PartialOrd::partial_cmp(*self, *other)
2094 }
2095 #[inline]
2096 fn lt(&self, other: &&mut B) -> bool {
2097 PartialOrd::lt(*self, *other)
2098 }
2099 #[inline]
2100 fn le(&self, other: &&mut B) -> bool {
2101 PartialOrd::le(*self, *other)
2102 }
2103 #[inline]
2104 fn gt(&self, other: &&mut B) -> bool {
2105 PartialOrd::gt(*self, *other)
2106 }
2107 #[inline]
2108 fn ge(&self, other: &&mut B) -> bool {
2109 PartialOrd::ge(*self, *other)
2110 }
2111 }
2112 #[stable(feature = "rust1", since = "1.0.0")]
2113 impl<A: ?Sized> Ord for &mut A
2114 where
2115 A: Ord,
2116 {
2117 #[inline]
2118 fn cmp(&self, other: &Self) -> Ordering {
2119 Ord::cmp(*self, *other)
2120 }
2121 }
2122 #[stable(feature = "rust1", since = "1.0.0")]
2123 impl<A: ?Sized> Eq for &mut A where A: Eq {}
2124
2125 #[stable(feature = "rust1", since = "1.0.0")]
2126 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A
2127 where
2128 A: PartialEq<B>,
2129 {
2130 #[inline]
2131 fn eq(&self, other: &&mut B) -> bool {
2132 PartialEq::eq(*self, *other)
2133 }
2134 #[inline]
2135 fn ne(&self, other: &&mut B) -> bool {
2136 PartialEq::ne(*self, *other)
2137 }
2138 }
2139
2140 #[stable(feature = "rust1", since = "1.0.0")]
2141 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A
2142 where
2143 A: PartialEq<B>,
2144 {
2145 #[inline]
2146 fn eq(&self, other: &&B) -> bool {
2147 PartialEq::eq(*self, *other)
2148 }
2149 #[inline]
2150 fn ne(&self, other: &&B) -> bool {
2151 PartialEq::ne(*self, *other)
2152 }
2153 }
2154}
2155