macros.rs.html -- source
Description: Source to the Rust file `src/liballoc/macros.rs`.
Keywords: rust, rustlang, rust-lang

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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)*)))
    }