sumtype 0.4.0

Generate zerocost anonymous sum types that implement common traits
Documentation 
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// `repeat().take()` matches the explicit `Take<Repeat<_>>` types named in the `sumtype!` calls.
#![allow(clippy::manual_repeat_n)]
use sumtype::sumtype;

#[allow(unused)]
trait MyTrait {
    type Ty<'a, T>
    where
        T: 'a;

    fn f<'a, T>(i: usize, _: &'a T) -> Self::Ty<'a, T>;
}

#[sumtype(sumtype::traits::Iterator)]
impl MyTrait for () {
    type Ty<'a, T> = sumtype!['a, T] where T: 'a;
    fn f<'a, T>(i: usize, t: &'a T) -> Self::Ty<'a, T> {
        if i == 0 {
            sumtype!(std::iter::empty(), for<'a, T: 'a> std::iter::Empty<&'a T>)
        } else {
            sumtype!(
                std::iter::repeat(t).take(i),
                for<'a, T: 'a> std::iter::Take<std::iter::Repeat<&'a T>>
            )
        }
    }
}

#[allow(unused)]
trait MyTrait2<T> {
    type Ty<'a>
    where
        T: 'a;

    fn f<'a>(i: usize, _: &'a T) -> Self::Ty<'a>;
}

#[sumtype(sumtype::traits::Iterator)]
impl<T> MyTrait2<T> for () {
    type Ty<'a> = sumtype!['a] where T: 'a;
    fn f<'a>(i: usize, t: &'a T) -> Self::Ty<'a> {
        if i == 0 {
            sumtype!(std::iter::empty(), for<'a> std::iter::Empty<&'a T> where T: 'a)
        } else {
            sumtype!(
                std::iter::repeat(t).take(i),
                for<'a> std::iter::Take<std::iter::Repeat<&'a T>>
                where T: 'a
            )
        }
    }
}