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/// 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(not(test))] #[doc(alias = "alloc")] #[doc(alias = "malloc")] #[macro_export] #[stable(feature = "rust1", since = "1.0.0")] #[allow_internal_unstable(box_syntax, 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),+ $(,)?) => ( $crate::__rust_force_expr!(<[_]>::into_vec(box [$($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(test)] macro_rules! vec { () => ( $crate::vec::Vec::new() ); ($elem:expr; $n:expr) => ( $crate::vec::from_elem($elem, $n) ); ($($x:expr),*) => ( $crate::slice::into_vec(box [$($x),*]) ); ($($x:expr,)*) => (vec![$($x),*]) } /// Creates a `String` using interpolation of runtime expressions. /// /// The first argument `format!` receives is a format string. This must be a string /// literal. The power of the formatting string is in the `{}`s contained. /// /// Additional parameters passed to `format!` replace the `{}`s within the /// formatting string in the order given unless named or positional parameters /// are used; see [`std::fmt`] for more information. /// /// A common use for `format!` is concatenation and interpolation of strings. /// The same convention is used with [`print!`] and [`write!`] macros, /// depending on the intended destination of the string. /// /// To convert a single value to a string, use the [`to_string`] method. This /// will use the [`Display`] formatting trait. /// /// [`std::fmt`]: ../std/fmt/index.html /// [`print!`]: ../std/macro.print.html /// [`write!`]: core::write /// [`to_string`]: crate::string::ToString /// [`Display`]: core::fmt::Display /// /// # Panics /// /// `format!` panics if a formatting trait implementation returns an error. /// This indicates an incorrect implementation /// since `fmt::Write for String` never returns an error itself. /// /// # Examples /// /// ``` /// format!("test"); /// format!("hello {}", "world!"); /// format!("x = {}, y = {y}", 10, y = 30); /// ``` #[macro_export] #[stable(feature = "rust1", since = "1.0.0")] macro_rules! format { ($($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 }; }