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#![no_std]
#[macro_export]
macro_rules! has_impl {
($ty:ty: $tr:path) => {
{
struct Test<T: ?Sized>(core::marker::PhantomData<T>);
#[allow(dead_code)]
impl<T: ?Sized + $tr> Test<T> {
const HAS_IMPL: bool = true;
}
trait Fallback {
const HAS_IMPL: bool = false;
}
impl<T: ?Sized> Fallback for T {}
Test::<$ty>::HAS_IMPL
}
};
}
#[cfg(test)]
mod tests {
trait Foo {}
impl Foo for i32 {}
trait Bar {}
#[test]
fn basic() {
assert_eq!(has_impl!(i32: Foo), true);
assert_eq!(has_impl!(i32: Bar), false);
}
mod path {
pub(crate) trait Trait1 {}
pub(crate) trait Trait2 {}
}
impl path::Trait1 for i32 {}
#[test]
fn with_path() {
assert_eq!(has_impl!(i32: path::Trait1), true);
assert_eq!(has_impl!(i32: path::Trait2), false);
}
}