36 lines
743 B
Rust
36 lines
743 B
Rust
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//check-pass
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trait Yokeable<'a>: 'static {
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type Output: 'a;
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}
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trait IsCovariant<'a> {}
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struct Yoke<Y: for<'a> Yokeable<'a>> {
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data: Y,
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}
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impl<Y: for<'a> Yokeable<'a>> Yoke<Y> {
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fn project<Y2: for<'a> Yokeable<'a>>(&self, _f: for<'a> fn(<Y as Yokeable<'a>>::Output, &'a ())
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-> <Y2 as Yokeable<'a>>::Output) -> Yoke<Y2> {
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unimplemented!()
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}
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}
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fn _upcast<Y>(x: Yoke<Y>) -> Yoke<Box<dyn IsCovariant<'static> + 'static>> where
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Y: for<'a> Yokeable<'a>,
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for<'a> <Y as Yokeable<'a>>::Output: IsCovariant<'a>
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{
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x.project(|data, _| {
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Box::new(data)
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})
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}
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impl<'a> Yokeable<'a> for Box<dyn IsCovariant<'static> + 'static> {
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type Output = Box<dyn IsCovariant<'a> + 'a>;
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}
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fn main() {}
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