assert-impl-trait

This crate provides a simple assert_impl macro for making compile-time assertions that a type implements a given trait.

The macro supports generic parameters via for<...> syntax and trait bounds via where ... syntax.

The macro is useful for crates that need tests to ensure their types implement the correct traits, and is aspecially useful if those types contain generics.

The macro can also be used to assert that a trait is dyn-compatible.

Examples

use assert_impl_trait::assert_impl;

// Assert that `u8` implements `Clone`.
assert_impl!(u8: Clone);

// Assert that for any type `T` that implements `Clone`, `Vec<T>` also
// implements `Clone`.
assert_impl!(
    for<T: Clone> {
        Vec<T>: Clone,
    }
);

// Assert that for any type `T` and any integer `N`:
// - If `T` implements `Clone`, `[T; N]` also implements `Clone`.
// - If `T` implements `Copy`, `[T; N]` also implements `Copy`.
// - If `T` is valid for a lifetime, `[T; N]` is also valid for it.
assert_impl!(
    for<T, const N: usize> {
        where T: Clone {
            [T; N]: Clone,
        }
        where T: Copy {
            [T; N]: Copy,
        }

        for<'a> where T: 'a {
            [T; N]: 'a,
        }
    }
);

// Assert that `Debug` is a dyn-compatible trait.
assert_impl!(dyn core::fmt::Debug:);

Usage

Add this to your Cargo.toml:

[dependencies]
assert-impl-trait = "1.0.0"

Dependencies

This crate depends on proc-macro2 and quote.

License

Licensed under either Apache License Version 2.0 or MIT license at your option.