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23 lines
508 B
Rust
23 lines
508 B
Rust
#![feature(fn_traits, unboxed_closures)]
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fn test<F: for<'x> FnOnce<(&'x str,)>>(_: F) {}
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struct Compose<F, G>(F, G);
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impl<T, F, G> FnOnce<(T,)> for Compose<F, G>
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where
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F: FnOnce<(T,)>,
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G: FnOnce<(F::Output,)>,
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{
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type Output = G::Output;
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extern "rust-call" fn call_once(self, (x,): (T,)) -> G::Output {
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(self.1)((self.0)(x))
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}
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}
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fn bad<T>(f: fn(&'static str) -> T) {
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test(Compose(f, |_| {}));
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//~^ ERROR: implementation of `FnOnce` is not general enough
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}
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fn main() {}
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