enum-ptr
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Ergonomic tagged pointer
Enum Ptr
0.2.0 beta is released with a lot of new features. I need feedback from community.
This crate provides a custom derive macro EnumPtr
to generate bridges between an enum T
and Compact<T>
with minimum cost. Compact<T>
is the compact representation of T
, and it is only one pointer wide.
For example, the following code
use enum_ptr::EnumPtr;
#[derive(EnumPtr)]
#[repr(C, usize)]
enum Foo<'a> {
A(&'a i32),
B(Box<i32>),
}
will generate
impl<'a> From<Foo<'a>> for Compact<Foo<'a>> {
// ...
}
impl<'a> From<Compact<Foo<'a>>> for Foo<'a> {
// ...
}
Since &i32
and Box<i32>
are aligned by 4 bytes, the lowest 2 bits of them are always zeros. Compact<Foo<'a>>
utilizes these bits to store the tag (discriminant).
Features
- No need to write unsafe pointer operations
- Supports various types and can be extended
- Supports
no_std
- Minimum type conversion cost
- Passes
cargo +nightly miri test
with strict provenance enabled.
Testing
$ cargo test
$ cargo +nightly miri test
Credits
- Thanks to @oxalica for reviewing this crate and providing a lot of helpful suggestions.
License
This project is licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.