Can't construct type alias for tuple struct

[philipc]

The following code fails to compile, but it seems correct to me:

struct Foo(u32);
type Bar = Foo;

fn main() {
    let foo = Foo(1);
    let bar = Bar(2);
    // error[E0423]: expected function, found type alias `Bar`
}

One alternative is use Foo as Bar;, but that doesn't allow me to give a different doc comment for Bar.

#42601 is a closely related issue (or even the same).

Meta

rustc 1.18.0 (03fc9d6 2017-06-06)
binary: rustc
commit-hash: 03fc9d6
commit-date: 2017-06-06
host: x86_64-unknown-linux-gnu
release: 1.18.0
LLVM version: 3.9

[petrochenkov]

This is a duplicate of several previously closed issues.

type Bar = Foo; is a type alias, it defines a name only in type namespace and doesn't know anything about the constructor function associated with Foo.

I don't think type can be changed to introduce names into value namespace now, so this issue is unlikely to be fixed as is (#42601 is a bit different because Self is reserved and currently unused in value namespace, so we can make it resolve to the constructor function when used in value context).

If we had fn aliases in addition to type aliases you could write something like fn Bar = Foo; to alias the constructor. For now fn Bar(arg: u32) -> Bar { Foo(arg) } can be used (possibly combined with type Bar = Foo; into a convenience macro).