1/// Creates a [`Vec`] containing the arguments.
2///
3/// `vec!` allows `Vec`s to be defined with the same syntax as array expressions.
4/// There are two forms of this macro:
5///
6/// - Create a [`Vec`] containing a given list of elements:
7///
8/// ```
9/// let v = vec![1, 2, 3];
10/// assert_eq!(v[0], 1);
11/// assert_eq!(v[1], 2);
12/// assert_eq!(v[2], 3);
13/// ```
14///
15/// - Create a [`Vec`] from a given element and size:
16///
17/// ```
18/// let v = vec![1; 3];
19/// assert_eq!(v, [1, 1, 1]);
20/// ```
21///
22/// Note that unlike array expressions this syntax supports all elements
23/// which implement [`Clone`] and the number of elements doesn't have to be
24/// a constant.
25///
26/// This will use `clone` to duplicate an expression, so one should be careful
27/// using this with types having a nonstandard `Clone` implementation. For
28/// example, `vec![Rc::new(1); 5]` will create a vector of five references
29/// to the same boxed integer value, not five references pointing to independently
30/// boxed integers.
31///
32/// Also, note that `vec![expr; 0]` is allowed, and produces an empty vector.
33/// This will still evaluate `expr`, however, and immediately drop the resulting value, so
34/// be mindful of side effects.
35///
36/// [`Vec`]: crate::vec::Vec
37#[cfg(all(not(no_global_oom_handling), not(test)))]
38#[macro_export]
39#[stable(feature = "rust1", since = "1.0.0")]
40#[rustc_diagnostic_item = "vec_macro"]
41#[allow_internal_unstable(rustc_attrs, liballoc_internals)]
42macro_rules! vec {
43 () => (
44 $crate::__rust_force_expr!($crate::vec::Vec::new())
45 );
46 ($elem:expr; $n:expr) => (
47 $crate::__rust_force_expr!($crate::vec::from_elem($elem, $n))
48 );
49 ($($x:expr),+ $(,)?) => (
50 $crate::__rust_force_expr!(<[_]>::into_vec(
51 // This rustc_box is not required, but it produces a dramatic improvement in compile
52 // time when constructing arrays with many elements.
53 #[rustc_box]
54 $crate::boxed::Box::new([$($x),+])
55 ))
56 );
57}
58
59// HACK(japaric): with cfg(test) the inherent `[T]::into_vec` method, which is
60// required for this macro definition, is not available. Instead use the
61// `slice::into_vec` function which is only available with cfg(test)
62// NB see the slice::hack module in slice.rs for more information
63#[cfg(all(not(no_global_oom_handling), test))]
64#[allow(unused_macro_rules)]
65macro_rules! vec {
66 () => (
67 $crate::vec::Vec::new()
68 );
69 ($elem:expr; $n:expr) => (
70 $crate::vec::from_elem($elem, $n)
71 );
72 ($($x:expr),*) => (
73 $crate::slice::into_vec($crate::boxed::Box::new([$($x),*]))
74 );
75 ($($x:expr,)*) => (vec![$($x),*])
76}
77
78/// Creates a `String` using interpolation of runtime expressions.
79///
80/// The first argument `format!` receives is a format string. This must be a string
81/// literal. The power of the formatting string is in the `{}`s contained.
82/// Additional parameters passed to `format!` replace the `{}`s within the
83/// formatting string in the order given unless named or positional parameters
84/// are used.
85///
86/// See [the formatting syntax documentation in `std::fmt`](../std/fmt/index.html)
87/// for details.
88///
89/// A common use for `format!` is concatenation and interpolation of strings.
90/// The same convention is used with [`print!`] and [`write!`] macros,
91/// depending on the intended destination of the string; all these macros internally use [`format_args!`].
92///
93/// To convert a single value to a string, use the [`to_string`] method. This
94/// will use the [`Display`] formatting trait.
95///
96/// To concatenate literals into a `&'static str`, use the [`concat!`] macro.
97///
98/// [`print!`]: ../std/macro.print.html
99/// [`write!`]: core::write
100/// [`format_args!`]: core::format_args
101/// [`to_string`]: crate::string::ToString
102/// [`Display`]: core::fmt::Display
103/// [`concat!`]: core::concat
104///
105/// # Panics
106///
107/// `format!` panics if a formatting trait implementation returns an error.
108/// This indicates an incorrect implementation
109/// since `fmt::Write for String` never returns an error itself.
110///
111/// # Examples
112///
113/// ```
114/// format!("test"); // => "test"
115/// format!("hello {}", "world!"); // => "hello world!"
116/// format!("x = {}, y = {val}", 10, val = 30); // => "x = 10, y = 30"
117/// let (x, y) = (1, 2);
118/// format!("{x} + {y} = 3"); // => "1 + 2 = 3"
119/// ```
120#[macro_export]
121#[stable(feature = "rust1", since = "1.0.0")]
122#[cfg_attr(not(test), rustc_diagnostic_item = "format_macro")]
123macro_rules! format {
124 ($($arg:tt)*) => {{
125 let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
126 res
127 }}
128}
129
130/// Force AST node to an expression to improve diagnostics in pattern position.
131#[doc(hidden)]
132#[macro_export]
133#[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")]
134macro_rules! __rust_force_expr {
135 ($e:expr) => {
136 $e
137 };
138}
139