class A {} protocol BProtocol { associatedtype Info: A var info: Info? { get set } } class B<T1: A>: BProtocol { var info: T1? } protocol CProtocol { associatedtype Property: BProtocol var property: Property? { get set } } // vvvvvvvv ここが違う class C<T2 : BProtocol>: CProtocol { var property: T2? } (edited)