]>
git.proxmox.com Git - rustc.git/blob - src/liballoc/macros.rs
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 /// [`Vec`]: ../std/vec/struct.Vec.html
33 /// [`Clone`]: ../std/clone/trait.Clone.html
36 #[stable(feature = "rust1", since = "1.0.0")]
37 #[allow_internal_unstable(box_syntax)]
40 $
crate::vec
::Vec
::new()
42 ($elem
:expr
; $n
:expr
) => (
43 $
crate::vec
::from_elem($elem
, $n
)
45 ($
($x
:expr
),+ $
(,)?
) => (
46 <[_
]>::into_vec(box [$
($x
),+])
50 // HACK(japaric): with cfg(test) the inherent `[T]::into_vec` method, which is
51 // required for this macro definition, is not available. Instead use the
52 // `slice::into_vec` function which is only available with cfg(test)
53 // NB see the slice::hack module in slice.rs for more information
57 $
crate::vec
::Vec
::new()
59 ($elem
:expr
; $n
:expr
) => (
60 $
crate::vec
::from_elem($elem
, $n
)
63 $
crate::slice
::into_vec(box [$
($x
),*])
65 ($
($x
:expr
,)*) => (vec
![$
($x
),*])
68 /// Creates a `String` using interpolation of runtime expressions.
70 /// The first argument `format!` receives is a format string. This must be a string
71 /// literal. The power of the formatting string is in the `{}`s contained.
73 /// Additional parameters passed to `format!` replace the `{}`s within the
74 /// formatting string in the order given unless named or positional parameters
75 /// are used; see [`std::fmt`][fmt] for more information.
77 /// A common use for `format!` is concatenation and interpolation of strings.
78 /// The same convention is used with [`print!`] and [`write!`] macros,
79 /// depending on the intended destination of the string.
81 /// To convert a single value to a string, use the [`to_string`] method. This
82 /// will use the [`Display`] formatting trait.
84 /// [fmt]: ../std/fmt/index.html
85 /// [`print!`]: ../std/macro.print.html
86 /// [`write!`]: ../std/macro.write.html
87 /// [`to_string`]: ../std/string/trait.ToString.html
88 /// [`Display`]: ../std/fmt/trait.Display.html
92 /// `format!` panics if a formatting trait implementation returns an error.
93 /// This indicates an incorrect implementation
94 /// since `fmt::Write for String` never returns an error itself.
100 /// format!("hello {}", "world!");
101 /// format!("x = {}, y = {y}", 10, y = 30);
104 #[stable(feature = "rust1", since = "1.0.0")]
105 macro_rules
! format
{
107 let res
= $
crate::fmt
::format($
crate::__export
::format_args
!($
($arg
)*));