| /// 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); |
| /// let (x, y) = (1, 2); |
| /// format!("{x} + {y} = 3"); |
| /// ``` |
| #[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 |
| }; |
| } |