ConstrainToEnum.swift

// MARK: Types:

protocol EnumType {

}

protocol MyProtocol {
    associatedtype SomeType: EnumType

    func foo(bar: SomeType)
}


// MARK: Working example:

enum MyConformingEnum: EnumType {
    case Foo
    case Bar
}


struct MyWorkingStruct: MyProtocol {
    func foo(bar: MyConformingEnum) {

    }

}



// MARK: Non-working example:

enum MyNonConformingEnum {
    case Foo
    case Bar
}

struct MyNonWorkingStruct: MyProtocol {
    func foo(bar: MyNonConformingEnum) {

    }
}