// Works
class BaseClass {
    required init() {}
}
// Doesn't work
//class ParentOfBaseClass {}
//class BaseClass: ParentOfBaseClass {
//    required override init() {}
//}

protocol StringConstructible where Self: BaseClass
{
    init(string: String)
    static func makeFromString(_ string: String) -> Self
}

class ConcreteClass: BaseClass, StringConstructible
{
    required init() {
    }

    required init(string: String) {
    }

    static func makeFromString(_ string: String) -> Self {
        return self.init(string: string)
    }
}

extension StringConstructible
{
    // Doesn't compile if `BaseClass` has a parent class. The compiler
    // doesn't "see" the custom initializer and uses `init()` instead.
    // The error is: "argument passed to call that takes no arguments".
    func failingTest() {
        _ = Self.init(string: "")
    }

    // Compiles in all cases.
    func passingTest() {
        _ = Self.makeFromString("")
    }
}

// Same as above with generics. This was the initially intended construct.
func failingTest<T>(input: T) where T: StringConstructible {
    _ = T.init(string: "")
}
func passingTest<T>(input: T) where T: StringConstructible {
    _ = T.makeFromString("")
}