Crate generic_statics

A “workaround” for missing generic statics in Rust.

This crate is experimental and might not be fully sound. Use at your own risk.

The core functionality is provided by Namespace::generic_static.

use std::sync::atomic::{AtomicPtr, Ordering};
use generic_statics::{define_namespace, Namespace};

define_namespace!(Test);

let a = Test::generic_static::<AtomicPtr<usize>>().load(Ordering::Relaxed);

Caveats and Limitations

This crate is nightly only and relies on #![feature(asm_const)].

The generic statics provided by this crate use static allocation (i.e. no dynamic allocation will occur at runtime) and is almost zero-cost (aside from some inline asm instructions for computing the static address).

However, this crate is only best-effort (i.e. best-effort stable addresses):

use generic_statics::{define_namespace, Namespace};

define_namespace!(Test);

// This is *not* guaranteed, but in usual cases this will work just fine.
assert_eq!(
    Test::generic_static::<usize>() as *const _,
    Test::generic_static::<usize>() as *const _
);

The used approach relies on inline assembly to instantiate/reserve static data for each monomorphized variant of the function. Unfortunately inlining will return a different version of the data and thus will not return stable addresses. However, Namespace::generic_static is marked #[inline(never)] which should provide stable addresses in most situations (Note that #[inline(never)] is just a hint to the compiler and doesn’t guarantee anything).

Only “zeroable” types are allowed for now due to inline asm restrictions.

This crate only supports these targets for now:

• macOS x86_64, aarch64
• Linux x86_64, aarch64
• FreeBSD x86_64, aarch64
• Windows x86_64

Macros

define_namespace

Traits

Namespace

A namespace for generic statics.

Zeroable

Types that can be safely “zero-initialized”.