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Diffstat (limited to '')
| -rw-r--r-- | library/alloc/src/macros.rs | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/library/alloc/src/macros.rs b/library/alloc/src/macros.rs new file mode 100644 index 000000000..88eb6aa7a --- /dev/null +++ b/library/alloc/src/macros.rs @@ -0,0 +1,129 @@ +/// Creates a [`Vec`] containing the arguments. +/// +/// `vec!` allows `Vec`s to be defined with the same syntax as array expressions. +/// There are two forms of this macro: +/// +/// - Create a [`Vec`] containing a given list of elements: +/// +/// ``` +/// let v = vec![1, 2, 3]; +/// assert_eq!(v[0], 1); +/// assert_eq!(v[1], 2); +/// assert_eq!(v[2], 3); +/// ``` +/// +/// - Create a [`Vec`] from a given element and size: +/// +/// ``` +/// let v = vec![1; 3]; +/// assert_eq!(v, [1, 1, 1]); +/// ``` +/// +/// Note that unlike array expressions this syntax supports all elements +/// which implement [`Clone`] and the number of elements doesn't have to be +/// a constant. +/// +/// This will use `clone` to duplicate an expression, so one should be careful +/// using this with types having a nonstandard `Clone` implementation. For +/// example, `vec![Rc::new(1); 5]` will create a vector of five references +/// to the same boxed integer value, not five references pointing to independently +/// boxed integers. +/// +/// Also, note that `vec![expr; 0]` is allowed, and produces an empty vector. +/// This will still evaluate `expr`, however, and immediately drop the resulting value, so +/// be mindful of side effects. +/// +/// [`Vec`]: crate::vec::Vec +#[cfg(all(not(no_global_oom_handling), not(test)))] +#[macro_export] +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_diagnostic_item = "vec_macro"] +#[allow_internal_unstable(rustc_attrs, liballoc_internals)] +macro_rules! vec { + () => ( + $crate::__rust_force_expr!($crate::vec::Vec::new()) + ); + ($elem:expr; $n:expr) => ( + $crate::__rust_force_expr!($crate::vec::from_elem($elem, $n)) + ); + ($($x:expr),+ $(,)?) => ( + $crate::__rust_force_expr!(<[_]>::into_vec( + #[rustc_box] + $crate::boxed::Box::new([$($x),+]) + )) + ); +} + +// HACK(japaric): with cfg(test) the inherent `[T]::into_vec` method, which is +// required for this macro definition, is not available. Instead use the +// `slice::into_vec` function which is only available with cfg(test) +// NB see the slice::hack module in slice.rs for more information +#[cfg(all(not(no_global_oom_handling), test))] +#[allow(unused_macro_rules)] +macro_rules! vec { + () => ( + $crate::vec::Vec::new() + ); + ($elem:expr; $n:expr) => ( + $crate::vec::from_elem($elem, $n) + ); + ($($x:expr),*) => ( + $crate::slice::into_vec($crate::boxed::Box::new([$($x),*])) + ); + ($($x:expr,)*) => (vec![$($x),*]) +} + +/// Creates a `String` using interpolation of runtime expressions. +/// +/// The first argument `format!` receives is a format string. This must be a string +/// literal. The power of the formatting string is in the `{}`s contained. +/// +/// Additional parameters passed to `format!` replace the `{}`s within the +/// formatting string in the order given unless named or positional parameters +/// are used; see [`std::fmt`] for more information. +/// +/// A common use for `format!` is concatenation and interpolation of strings. +/// The same convention is used with [`print!`] and [`write!`] macros, +/// depending on the intended destination of the string. +/// +/// To convert a single value to a string, use the [`to_string`] method. This +/// will use the [`Display`] formatting trait. +/// +/// [`std::fmt`]: ../std/fmt/index.html +/// [`print!`]: ../std/macro.print.html +/// [`write!`]: core::write +/// [`to_string`]: crate::string::ToString +/// [`Display`]: core::fmt::Display +/// +/// # Panics +/// +/// `format!` panics if a formatting trait implementation returns an error. +/// This indicates an incorrect implementation +/// since `fmt::Write for String` never returns an error itself. +/// +/// # Examples +/// +/// ``` +/// format!("test"); +/// format!("hello {}", "world!"); +/// format!("x = {}, y = {y}", 10, y = 30); +/// ``` +#[macro_export] +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(test), rustc_diagnostic_item = "format_macro")] +macro_rules! format { + ($($arg:tt)*) => {{ + let res = $crate::fmt::format($crate::__export::format_args!($($arg)*)); + res + }} +} + +/// Force AST node to an expression to improve diagnostics in pattern position. +#[doc(hidden)] +#[macro_export] +#[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")] +macro_rules! __rust_force_expr { + ($e:expr) => { + $e + }; +} |