cd658a30ef
- async closure Output deduction, solver cycle step kinds from the goal source, object supertrait projections, impl candidate merging, trait supertrait well-formedness, E0282 for casts and method calls on diverging variables, the (..) tuple pattern Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
21 lines
768 B
Rust
21 lines
768 B
Rust
// A trait object whose principal's supertrait fixes an associated type (`Foo: Sup<A = u8>`,
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// `Cb: Fn(i32) -> i32`) implements the supertrait: the object candidate's requirements see the
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// fixed projections (rustc lowers them into the object type), so no solver cycle arises.
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trait Sup { type A; fn get(&self) -> Self::A; }
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trait Foo: Sup<A = u8> {}
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struct S;
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impl Sup for S { type A = u8; fn get(&self) -> u8 { 7 } }
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impl Foo for S {}
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fn needs_sup<T: Sup + ?Sized>(_: &T) -> bool { true }
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trait Cb: Fn(i32) -> i32 {}
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impl<T: Fn(i32) -> i32> Cb for T {}
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fn call(f: Box<dyn Cb>) -> i32 { f(42) }
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#[test]
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fn supertrait_projections() {
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let f: &dyn Foo = &S;
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assert!(needs_sup(f));
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assert_eq!(f.get(), 7);
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assert_eq!(call(Box::new(|x| x + 1)), 43);
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}
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