protocol Foo {
    associatedtype F
}

class FooClass : Foo {
    typealias F = String
}

class Bar<F:Foo> {
    let foo: F

    init(){
        // Error, cannot assign value of type 'FooClass' to type 'F'
        foo = FooClass()
    }
}

func weird<F:Foo>(_ f: F){ }

func test(){
    weird(FooClass()) // this works
}

class Bar<F:Foo> {
    let foo: FooClass.F

    init(){
        foo = FooClass.F()
    }
}

class Bar<F:Foo> {
    let foo: FooClass

    init(){
        foo = FooClass()
    }
}