commit | 37f9979326e642c817a1add6fdfad2d3440fbaf7 | [log] [tgz] |
---|---|---|
author | Andrew Walbran <qwandor@google.com> | Mon May 13 17:40:59 2024 +0100 |
committer | Andrew Walbran <qwandor@google.com> | Mon May 13 17:40:59 2024 +0100 |
tree | 669184d9c9306c968495f0fa3fcdbf45ece114ce | |
parent | 18c97b333ddc56692d5a2bd1dab3901ef2543283 [diff] |
Re-run cargo_embargo to remove duplicate cfgs. Test: Looked at output Android.bp. Change-Id: I83c2510231a3f337ac5c346b7129feae27e43ed9
C-Like offset_of
functionality for Rust structs.
Introduces the following macros:
offset_of!
for obtaining the offset of a member of a struct.offset_of_tuple!
for obtaining the offset of a member of a tuple. (Requires Rust 1.20+)offset_of_union!
for obtaining the offset of a member of a union.span_of!
for obtaining the range that a field, or fields, span.memoffset
works under no_std
environments.
Add the following dependency to your Cargo.toml
:
[dependencies] memoffset = "0.8"
These versions will compile fine with rustc versions greater or equal to 1.19.
use memoffset::{offset_of, span_of}; #[repr(C, packed)] struct Foo { a: u32, b: u32, c: [u8; 5], d: u32, } fn main() { assert_eq!(offset_of!(Foo, b), 4); assert_eq!(offset_of!(Foo, d), 4+4+5); assert_eq!(span_of!(Foo, a), 0..4); assert_eq!(span_of!(Foo, a .. c), 0..8); assert_eq!(span_of!(Foo, a ..= c), 0..13); assert_eq!(span_of!(Foo, ..= d), 0..17); assert_eq!(span_of!(Foo, b ..), 4..17); }
memoffset
has support for compile-time offset_of!
on rust>=1.65, or on older nightly compilers.
Constant evaluation is automatically enabled and avilable on stable compilers starting with rustc 1.65.
This is an incomplete implementation with one caveat: Due to dependence on #![feature(const_refs_to_cell)]
, you cannot get the offset of a Cell
field in a const-context.
This means that if need to get the offset of a cell, you'll have to remain on nightly for now.
If you‘re using a new-enough nightly and you require the ability to get the offset of a Cell
, you’ll have to enable the unstable_const
cargo feature, as well as enabling const_refs_to_cell
in your crate root.
Do note that unstable_const
is an unstable feature that is set to be removed in a future version of memoffset
.
Cargo.toml:
[dependencies.memoffset] version = "0.8" features = ["unstable_const"]
Your crate root: (lib.rs
/main.rs
)
#![feature(const_refs_to_cell)]
In order to use it on an older nightly compiler, you must enable the unstable_const
crate feature and several compiler features.
Your crate root: (lib.rs
/main.rs
)
#![feature(const_ptr_offset_from, const_refs_to_cell)]