vendor/memoffset/README.md

   1 # memoffset #
   2
   3 [![](https://img.shields.io/crates/v/memoffset.svg)](https://crates.io/crates/memoffset)
   4
   5 C-Like `offset_of` functionality for Rust structs.
   6
   7 Introduces the following macros:
   8  * `offset_of!` for obtaining the offset of a member of a struct.
   9  * `offset_of_tuple!` for obtaining the offset of a member of a tuple. (Requires Rust 1.20+)
  10  * `span_of!` for obtaining the range that a field, or fields, span.
  11
  12 `memoffset` works under `no_std` environments.
  13
  14 ## Usage ##
  15 Add the following dependency to your `Cargo.toml`:
  16
  17 ```toml
  18 [dependencies]
  19 memoffset = "0.6"
  20 ```
  21
  22 These versions will compile fine with rustc versions greater or equal to 1.19.
  23
  24 ## Examples ##
  25 ```rust
  26 use memoffset::{offset_of, span_of};
  27
  28 #[repr(C, packed)]
  29 struct Foo {
  30     a: u32,
  31     b: u32,
  32     c: [u8; 5],
  33     d: u32,
  34 }
  35
  36 fn main() {
  37     assert_eq!(offset_of!(Foo, b), 4);
  38     assert_eq!(offset_of!(Foo, d), 4+4+5);
  39
  40     assert_eq!(span_of!(Foo, a),        0..4);
  41     assert_eq!(span_of!(Foo, a ..  c),  0..8);
  42     assert_eq!(span_of!(Foo, a ..= c),  0..13);
  43     assert_eq!(span_of!(Foo, ..= d),    0..17);
  44     assert_eq!(span_of!(Foo, b ..),     4..17);
  45 }
  46 ```
  47
  48 ## Feature flags ##
  49
  50 ### Usage in constants ###
  51 `memoffset` has **experimental** support for compile-time `offset_of!` on a nightly compiler.
  52
  53 In order to use it, you must enable the `unstable_const` crate feature and several compiler features.
  54
  55 Cargo.toml:
  56 ```toml
  57 [dependencies.memoffset]
  58 version = "0.6"
  59 features = ["unstable_const"]
  60 ```
  61
  62 Your crate root: (`lib.rs`/`main.rs`)
  63 ```rust,ignore
  64 #![feature(const_ptr_offset_from, const_refs_to_cell)]
  65 ```