[~OT] Go generics

language design
7

I am pretty sure that if Rust got anonymous types, the signature of foo would be something like.

fn foo(cond: bool) -> (i32 | &'static str);

Which open some really interesting design idea:

fn foo(cond: bool) -> impl Debug {
    // Automatically create an enum with two variant, so the value returned
    // by both branch of the `if` don't need to be the same.
    // Anonymous enum would implements all the trait implemented by all
    // the variants, so this anonymous variant would implement `Debug`.
    let ret: (i32 | &'static str) = if cond {
        42
    } else {
        "foo"
    }
    ret
}

And the compiler should probably at this point be smart enough to understand this:

fn foo(cond: bool) -> impl Debug {
    if cond {
        42 as i32
    } else {
        "foo"
    }
    // the type created by this `if` statement is an anonymous enum
    // of (i32 | &'static str). Both variants implements `Debug`, so the
    // anonymous enum would also implement `Debug`.
}