gecko-dev/third_party/rust/memoffset/README.md

memoffset

C-Like offset_of functionality for Rust structs.

Introduces the following macros:

• offset_of! for obtaining the offset of a member of a struct.
• span_of! for obtaining the range that a field, or fields, span.

memoffset works under no_std environments.

Usage

Add the following dependency to your Cargo.toml:

[dependencies]
memoffset = "0.2"

Add the following lines at the top of your main.rs or lib.rs files.

#[macro_use]
extern crate memoffset;

Examples

#[repr(C, packed)]
struct Foo {
	a: u32,
	b: u32,
	c: [u8; 5],
	d: u32,
}

assert_eq!(offset_of!(Foo, b), 4);
assert_eq!(offset_of!(Foo, c[3]), 11);

assert_eq!(span_of!(Foo, a),          0..4);
assert_eq!(span_of!(Foo, a ..  c),    0..8);
assert_eq!(span_of!(Foo, a ..  c[1]), 0..9);
assert_eq!(span_of!(Foo, a ..= c[1]), 0..10);
assert_eq!(span_of!(Foo, ..= d),      0..14);
assert_eq!(span_of!(Foo, b ..),       4..17);