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