library/alloc/src/macros.rs

   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), not(bootstrap)))]
  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)]
  42 macro_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             #[rustc_box]
  52             $crate::boxed::Box::new([$($x),+])
  53         ))
  54     );
  55 }
  56
  57 /// Creates a `Vec` containing the arguments (bootstrap version).
  58 #[cfg(all(not(no_global_oom_handling), not(test), bootstrap))]
  59 #[macro_export]
  60 #[stable(feature = "rust1", since = "1.0.0")]
  61 #[rustc_diagnostic_item = "vec_macro"]
  62 #[allow_internal_unstable(box_syntax, liballoc_internals)]
  63 macro_rules! vec {
  64     () => (
  65         $crate::__rust_force_expr!($crate::vec::Vec::new())
  66     );
  67     ($elem:expr; $n:expr) => (
  68         $crate::__rust_force_expr!($crate::vec::from_elem($elem, $n))
  69     );
  70     ($($x:expr),+ $(,)?) => (
  71         $crate::__rust_force_expr!(<[_]>::into_vec(box [$($x),+]))
  72     );
  73 }
  74
  75 // HACK(japaric): with cfg(test) the inherent `[T]::into_vec` method, which is
  76 // required for this macro definition, is not available. Instead use the
  77 // `slice::into_vec`  function which is only available with cfg(test)
  78 // NB see the slice::hack module in slice.rs for more information
  79 #[cfg(all(not(no_global_oom_handling), test))]
  80 #[allow(unused_macro_rules)]
  81 macro_rules! vec {
  82     () => (
  83         $crate::vec::Vec::new()
  84     );
  85     ($elem:expr; $n:expr) => (
  86         $crate::vec::from_elem($elem, $n)
  87     );
  88     ($($x:expr),*) => (
  89         $crate::slice::into_vec($crate::boxed::Box::new([$($x),*]))
  90     );
  91     ($($x:expr,)*) => (vec![$($x),*])
  92 }
  93
  94 /// Creates a `String` using interpolation of runtime expressions.
  95 ///
  96 /// The first argument `format!` receives is a format string. This must be a string
  97 /// literal. The power of the formatting string is in the `{}`s contained.
  98 ///
  99 /// Additional parameters passed to `format!` replace the `{}`s within the
 100 /// formatting string in the order given unless named or positional parameters
 101 /// are used; see [`std::fmt`] for more information.
 102 ///
 103 /// A common use for `format!` is concatenation and interpolation of strings.
 104 /// The same convention is used with [`print!`] and [`write!`] macros,
 105 /// depending on the intended destination of the string.
 106 ///
 107 /// To convert a single value to a string, use the [`to_string`] method. This
 108 /// will use the [`Display`] formatting trait.
 109 ///
 110 /// [`std::fmt`]: ../std/fmt/index.html
 111 /// [`print!`]: ../std/macro.print.html
 112 /// [`write!`]: core::write
 113 /// [`to_string`]: crate::string::ToString
 114 /// [`Display`]: core::fmt::Display
 115 ///
 116 /// # Panics
 117 ///
 118 /// `format!` panics if a formatting trait implementation returns an error.
 119 /// This indicates an incorrect implementation
 120 /// since `fmt::Write for String` never returns an error itself.
 121 ///
 122 /// # Examples
 123 ///
 124 /// ```
 125 /// format!("test");
 126 /// format!("hello {}", "world!");
 127 /// format!("x = {}, y = {y}", 10, y = 30);
 128 /// ```
 129 #[macro_export]
 130 #[stable(feature = "rust1", since = "1.0.0")]
 131 #[cfg_attr(not(test), rustc_diagnostic_item = "format_macro")]
 132 macro_rules! format {
 133     ($($arg:tt)*) => {{
 134         let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
 135         res
 136     }}
 137 }
 138
 139 /// Force AST node to an expression to improve diagnostics in pattern position.
 140 #[doc(hidden)]
 141 #[macro_export]
 142 #[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")]
 143 macro_rules! __rust_force_expr {
 144     ($e:expr) => {
 145         $e
 146     };
 147 }