1 /// Creates a [`Vec`] containing the arguments.
3 /// `vec!` allows `Vec`s to be defined with the same syntax as array expressions.
4 /// There are two forms of this macro:
6 /// - Create a [`Vec`] containing a given list of elements:
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);
15 /// - Create a [`Vec`] from a given element and size:
18 /// let v = vec![1; 3];
19 /// assert_eq!(v, [1, 1, 1]);
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
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
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.
36 /// [`Vec`]: crate::vec::Vec
38 #[doc(alias = "alloc")]
39 #[doc(alias = "malloc")]
41 #[stable(feature = "rust1", since = "1.0.0")]
42 #[allow_internal_unstable(box_syntax, liballoc_internals)]
45 $crate::__rust_force_expr!($crate::vec::Vec::new())
47 ($elem:expr; $n:expr) => (
48 $crate::__rust_force_expr!($crate::vec::from_elem($elem, $n))
50 ($($x:expr),+ $(,)?) => (
51 $crate::__rust_force_expr!(<[_]>::into_vec(box [$($x),+]))
55 // HACK(japaric): with cfg(test) the inherent `[T]::into_vec` method, which is
56 // required for this macro definition, is not available. Instead use the
57 // `slice::into_vec` function which is only available with cfg(test)
58 // NB see the slice::hack module in slice.rs for more information
62 $crate::vec::Vec::new()
64 ($elem:expr; $n:expr) => (
65 $crate::vec::from_elem($elem, $n)
68 $crate::slice::into_vec(box [$($x),*])
70 ($($x:expr,)*) => (vec![$($x),*])
73 /// Creates a `String` using interpolation of runtime expressions.
75 /// The first argument `format!` receives is a format string. This must be a string
76 /// literal. The power of the formatting string is in the `{}`s contained.
78 /// Additional parameters passed to `format!` replace the `{}`s within the
79 /// formatting string in the order given unless named or positional parameters
80 /// are used; see [`std::fmt`] for more information.
82 /// A common use for `format!` is concatenation and interpolation of strings.
83 /// The same convention is used with [`print!`] and [`write!`] macros,
84 /// depending on the intended destination of the string.
86 /// To convert a single value to a string, use the [`to_string`] method. This
87 /// will use the [`Display`] formatting trait.
89 /// [`std::fmt`]: ../std/fmt/index.html
90 /// [`print!`]: ../std/macro.print.html
91 /// [`write!`]: core::write
92 /// [`to_string`]: crate::string::ToString
93 /// [`Display`]: core::fmt::Display
97 /// `format!` panics if a formatting trait implementation returns an error.
98 /// This indicates an incorrect implementation
99 /// since `fmt::Write for String` never returns an error itself.
105 /// format!("hello {}", "world!");
106 /// format!("x = {}, y = {y}", 10, y = 30);
109 #[stable(feature = "rust1", since = "1.0.0")]
110 #[cfg_attr(not(test), rustc_diagnostic_item = "format_macro")]
111 macro_rules! format {
113 let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
118 /// Force AST node to an expression to improve diagnostics in pattern position.
121 #[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")]
122 macro_rules! __rust_force_expr {