Freestanding associated types

[mversic]

Add support for freestanding associated types, i.e. types that don't comprise id like here:

use disjoint_impls::disjoint_impls;

pub trait Dispatch {
    type Group;
}

pub enum GroupA {}
impl Dispatch for (u16, u32) {
    type Group = GroupA;
}
impl Dispatch for (i16, i32) {
    type Group = GroupA;
}

pub enum GroupB {}
impl Dispatch for (i32, String) {
    type Group = GroupB;
}
impl Dispatch for (u32, String) {
    type Group = GroupB;
}

trait A {
    type B;
}

disjoint_impls! {
    pub trait Kita<U: A<B = u32>> {
        const NAME: &'static str;
    }

    impl<T, U, C> Kita<(U, C)> for T where (U, C): Dispatch<Group = GroupA> + A<B = u32> {
        const NAME: &'static str = "1st blanket A";
    }
    impl<T, U, C> Kita<(U, C)> for T where (U, C): Dispatch<Group = GroupB> + A<B = u32> {
        const NAME: &'static str = "1st blanket B";
    }

    impl<T: Dispatch<Group = GroupA>> Kita<(i32,)> for T {
        const NAME: &'static str = "2nd blanket A";
    }
    impl<T: Dispatch<Group = GroupB>> Kita<(i32,)> for T {
        const NAME: &'static str = "2nd blanket B";
    }
}

impl A for (i32,) {
    type B = u32;
}

fn main() {
    assert_eq!("Blanket A", <u32 as Kita<(u16, u32)>>::NAME);
}

This is associated type in trait definition. What if associated type is in the impl?