macros.rs.html -- source
Description: Source to the Rust file `/usr/obj/ports/rust-1.20.0/rustc-1.20.0-src/src/liballoc/macros.rs`.
Keywords: rust, rustlang, rust-lang

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    // Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    /// 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.
    #[cfg(not(test))]
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[allow_internal_unstable]
    macro_rules! vec {
        ($elem:expr; $n:expr) => (
            $crate::vec::from_elem($elem, $n)
        );
        ($($x:expr),*) => (
            <[_]>::into_vec(box [$($x),*])
        );
        ($($x:expr,)*) => (vec![$($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),*])
    }

    /// Use the syntax described in `std::fmt` to create a value of type `String`.
    /// See [`std::fmt`][fmt] for more information.
    ///
    /// [fmt]: ../std/fmt/index.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)*) => ($crate::fmt::format(format_args!($($arg)*)))
    }

    // Private macro to get the offset of a struct field in bytes from the address of the struct.
    macro_rules! offset_of {
        ($container:path, $field:ident) => {{
            // Make sure the field actually exists. This line ensures that a compile-time error is
            // generated if $field is accessed through a Deref impl.
            let $container { $field : _, .. };

            // Create an (invalid) instance of the container and calculate the offset to its
            // field. Using a null pointer might be UB if `&(*(0 as *const T)).field` is interpreted to
            // be nullptr deref.
            let invalid: $container = ::core::mem::uninitialized();
            let offset = &invalid.$field as *const _ as usize - &invalid as *const _ as usize;

            // Do not run destructors on the made up invalid instance.
            ::core::mem::forget(invalid);
            offset as isize
        }};
    }

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