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https://github.com/rust-lang/rust
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40 lines
1.2 KiB
Rust
40 lines
1.2 KiB
Rust
//@ revisions: old next
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//@[next] compile-flags: -Znext-solver
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//@ run-pass
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// A test for https://github.com/rust-lang/trait-system-refactor-initiative/issues/45.
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trait Trait {
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type Assoc: Into<u32>;
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}
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impl<T: Into<u32>> Trait for T {
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type Assoc = T;
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}
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fn prefer_alias_bound_projection<T: Trait>(x: T::Assoc) {
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// There are two possible types for `x`:
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// - `u32` by using the "alias bound" of `<T as Trait>::Assoc`
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// - `<T as Trait>::Assoc`, i.e. `u16`, by using `impl<T> From<T> for T`
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//
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// We infer the type of `x` to be `u32` here as it is highly likely
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// that this is expected by the user.
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let x = x.into();
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assert_eq!(std::mem::size_of_val(&x), 4);
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}
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fn impl_trait() -> impl Into<u32> {
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0u16
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}
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fn main() {
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// There are two possible types for `x`:
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// - `u32` by using the "alias bound" of `impl Into<u32>`
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// - `impl Into<u32>`, i.e. `u16`, by using `impl<T> From<T> for T`
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//
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// We infer the type of `x` to be `u32` here as it is highly likely
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// that this is expected by the user.
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let x = impl_trait().into();
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assert_eq!(std::mem::size_of_val(&x), 4);
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prefer_alias_bound_projection::<u16>(1);
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}
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