Associated types should permit arbitrary bounds

[carllerche]

Based on my understanding of the RFC, associated types should be able to specify bounds, yet the following does not work:

#![feature(associated_types)]

pub trait Cancel {
    fn cancel(self);
}

pub trait Foo {
    type C: Cancel;

    fn stuff(self) -> <Self as Foo>::C;
}

pub fn main() {
}

[tomjakubowski]

I'm not sure what the deal with that snippet was when the issue was opened, but it compiles today. The compiler also correctly rejects an impl of Foo which specifies a Foo::C type that does not fulfill Cancel, but you can't use that Cancel bound outside the trait (not sure if the function doit is supposed to be accepted):

#![feature(associated_types)]

pub trait Cancel {
    fn cancel(self);
}

pub trait Foo {
    type C: Cancel;

    fn stuff(self) -> <Self as Foo>::C;
    fn trait_doit(self) { // this method typechecks
        let cancel_me = self.stuff();
        cancel_me.cancel();
    }
}

fn doit<F: Foo>(f: F) { // this function doesn't typecheck
    let cancel_me = f.stuff();
    cancel_me.cancel();
}

pub fn main() {
}

<anon>:18:21: 18:30 error: the trait `Cancel` is not implemented for the type `C`
<anon>:18     let cancel_me = f.stuff();
                              ^~~~~~~~~
<anon>:19:15: 19:23 error: type `C` does not implement any method in scope named `cancel`
<anon>:19     cancel_me.cancel();
                        ^~~~~~~~
error: aborting due to 2 previous errors
playpen: application terminated with error code 101

[carllerche]

I'm pretty sure the fix for this landed.

[tomjakubowski]

I think my grievance is #18434