macros.rs.html -- source
Description: Source to the Rust file `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.

    // 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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