negative-impl
.
This crate emulates the unstable negative_impls feature
by generating a trait implementation with a condition that will never be true.
Usage
Add this to your Cargo.toml:
[dependencies]
negative-impl = "0.1"
Compiler support: requires rustc 1.37+
Examples
use negative_impl::negative_impl;
pub struct Type {}
#[negative_impl]
impl !Send for Type {}
#[negative_impl]
impl !Sync for Type {}
Supported traits
Currently this crate only supports auto traits.
-
Send -
Sync -
Unpin -
UnwindSafe -
RefUnwindSafe
Limitations
Conflicting implementations
The following code cannot compile due to impl<T: Send> Trait for T and
impl Trait for Type conflict.
use negative_impl::negative_impl;
pub struct Type {}
#[negative_impl]
impl !Send for Type {}
trait Trait {}
impl<T: Send> Trait for T {}
impl Trait for Type {}
error[E0119]: conflicting implementations of trait `Trait` for type `Type`:
--> src/lib.rs:60:1
|
14 | impl<T: Send> Trait for T {}
| ------------------------- first implementation here
15 | impl Trait for Type {}
| ^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Type`
The above code can be compiled using the unstable negative_impls feature.
#![feature(negative_impls)]
pub struct Type {}
impl !Send for Type {}
trait Trait {}
impl<T: Send> Trait for T {}
impl Trait for Type {}
Conditional negative impls
The current behavior of this crate with conditional negative impls is the
same as the unstable negative_impls feature, but
the unstable negative_impls feature plans to forbid it.
It's a great plan, but when it's implemented, this crate is unlikely to provide the same behavior due to the macro's limitation.
License
Licensed under either of Apache License, Version 2.0 or MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
