Lifetime parameters on an associated typed

lifetime_assoc_type.rs

extern crate typemap;

use typemap::Key;

struct Repository<'a, 'b> {
  one: SomeTypeThatHoldsAReference<'a>,
  two: SomeTypeThatHoldsAReference<'b>,
}

struct RepositoryState;

/// What's the correct syntax for specifying lifetime parameters
/// on an associated type in a trait implementation? Shown below
/// are the things I tried and the compiler errors each generated.

// error: wrong number of lifetime parameters: expected 2, found 0 [E0107]
//        type Value = Repository;
impl Key for RepositoryState {
    type Value = Repository;
}

// error: use of undeclared lifetime name `'a` [E0261]
//        type Value = Repository<'a, 'b>;
// error: use of undeclared lifetime name `'b` [E0261]
//        type Value = Repository<'a, 'b>;
impl Key for RepositoryState {
    type Value = Repository<'a, 'b>;
}

// error: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates [E0207]
//        impl<'a, 'b> Key for RepositoryState {
// error: the lifetime parameter `'b` is not constrained by the impl trait, self type, or predicates [E0207]
//        impl<'a, 'b> Key for RepositoryState {
impl<'a, 'b> Key for RepositoryState {
    type Value = Repository<'a, 'b>;
}

// error: ambiguous associated type; specify the type using the syntax `<Type as typemap::Key>::Value` [E0223]
//        impl<'a, 'b> Key for RepositoryState where Key::Value: 'a + 'b {
// error: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates [E0207]
//        impl<'a, 'b> Key for RepositoryState where Key::Value: 'a + 'b {
// error: the lifetime parameter `'b` is not constrained by the impl trait, self type, or predicates [E0207]
//        impl<'a, 'b> Key for RepositoryState where Key::Value: 'a + 'b {
impl<'a, 'b> Key for RepositoryState where Key::Value: 'a + 'b {
    type Value = Repository<'a, 'b>;
}

// error: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates [E0207]
//        impl<'a, 'b> Key for RepositoryState where <RepositoryState as Key>::Value: 'a + 'b {
// error: the lifetime parameter `'b` is not constrained by the impl trait, self type, or predicates [E0207]
//        impl<'a, 'b> Key for RepositoryState where <RepositoryState as Key>::Value: 'a + 'b {
impl<'a, 'b> Key for RepositoryState where <RepositoryState as Key>::Value: 'a + 'b {
    type Value = Repository<'a, 'b>;
}

// error: use of `Self` outside of an impl or trait [E0411]
//        impl<'a, 'b> Key for RepositoryState where <Self as Key>::Value: 'a + 'b {
impl<'a, 'b> Key for RepositoryState where <Self as Key>::Value: 'a + 'b {
    type Value = Repository<'a, 'b>;
}