Self alias as struct constructor

[durka]

Consider the following code

struct Foo { a: i32 }

impl Default for Foo {
    fn default() -> Self {
        Foo { a: 42 }
    }
}

We can't replace the last use of Foo in the impl with Self (you get E0071). But Self is a kind of type alias, or it acts like one anyway, and normally you can construct a struct through a type alias. So we should allow usage of Self like this.

brought up here cc @huonw

[KalitaAlexey]

Yes. I'd like to do it too.

[thepowersgang]

An alternative that I've been thinking of is allowing _ instead. (fitting in with a possible extension to enum matching)

[arielb1]

That's something I intended to implement.

[durka]

@arielb1 do you mean you don't think this requires an RFC?

[durka]

Implemented at rust-lang/rust#37035, thanks @petrochenkov!