[rustc.git] / src / test / ui / specialization / specialization-default-projection.rs

#![feature(specialization)] //~ WARN the feature `specialization` is incomplete

// Make sure we can't project defaulted associated types

trait Foo {
    type Assoc;
}

impl<T> Foo for T {
    default type Assoc = ();
}

impl Foo for u8 {
    type Assoc = String;
}

fn generic<T>() -> <T as Foo>::Assoc {
    // `T` could be some downstream crate type that specializes (or,
    // for that matter, `u8`).

    () //~ ERROR mismatched types
}

fn monomorphic() -> () {
    // Even though we know that `()` is not specialized in a
    // downstream crate, typeck refuses to project here.

    generic::<()>() //~ ERROR mismatched types
}

fn main() {
    // No error here, we CAN project from `u8`, as there is no `default`
    // in that impl.
    let s: String = generic::<u8>();
    println!("{}", s); // bad news if this all compiles
}
Commit	Line	Data
f035d41b	1	#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
54a0048b SL	2
	3	// Make sure we can't project defaulted associated types
	4
	5	trait Foo {
	6	type Assoc;
	7	}
	8
	9	impl<T> Foo for T {
	10	default type Assoc = ();
	11	}
	12
	13	impl Foo for u8 {
	14	type Assoc = String;
	15	}
	16
	17	fn generic<T>() -> <T as Foo>::Assoc {
	18	// `T` could be some downstream crate type that specializes (or,
	19	// for that matter, `u8`).
	20
	21	() //~ ERROR mismatched types
	22	}
	23
	24	fn monomorphic() -> () {
	25	// Even though we know that `()` is not specialized in a
	26	// downstream crate, typeck refuses to project here.
	27
	28	generic::<()>() //~ ERROR mismatched types
	29	}
	30
	31	fn main() {
	32	// No error here, we CAN project from `u8`, as there is no `default`
	33	// in that impl.
	34	let s: String = generic::<u8>();
	35	println!("{}", s); // bad news if this all compiles
	36	}