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Diffstat (limited to 'README.md')
| -rw-r--r-- | README.md | 32 |
1 files changed, 26 insertions, 6 deletions
@@ -7,6 +7,7 @@ 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. @@ -16,7 +17,7 @@ Add the following dependency to your `Cargo.toml`: ```toml [dependencies] -memoffset = "0.6" +memoffset = "0.8" ``` These versions will compile fine with rustc versions greater or equal to 1.19. @@ -45,21 +46,40 @@ fn main() { } ``` -## Feature flags ## +## Usage in constants ## +`memoffset` has support for compile-time `offset_of!` on rust>=1.65, or on older nightly compilers. -### Usage in constants ### -`memoffset` has **experimental** support for compile-time `offset_of!` on a nightly compiler. +### Usage on stable Rust ### +Constant evaluation is automatically enabled and avilable on stable compilers starting with rustc 1.65. -In order to use it, you must enable the `unstable_const` crate feature and several compiler features. +This is an incomplete implementation with one caveat: +Due to dependence on [`#![feature(const_refs_to_cell)]`](https://github.com/rust-lang/rust/issues/80384), 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. + +### Usage on recent nightlies ### + +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: ```toml [dependencies.memoffset] -version = "0.6" +version = "0.8" features = ["unstable_const"] ``` Your crate root: (`lib.rs`/`main.rs`) ```rust,ignore +#![feature(const_refs_to_cell)] +``` + +### Usage on older nightlies ### +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`) +```rust,ignore #![feature(const_ptr_offset_from, const_refs_to_cell)] ``` |