protocol MyProtocol: AnyObject { }
class MyClass { }
class MySubclass: MyClass, MyProtocol { }
class MyGenericClass<T> {
    func foo(with o: T) { }
}
extension MyGenericClass where T: MyClass {
    func bar(with o: T) { }
}
// this extension compiles. My understanding, though, is that it's treating the
// PCT as a protocol to conform to rather than a class to inherit from
extension MyGenericClass where T: MyClass & MyProtocol {
    func baz(with o: T) { }
}

// works fine; 'MySubclass' fills the requirement for 'MyClass & MyProtocol'
// in this context
var myClass: (MyClass & MyProtocol)?
myClass = MySubclass()

let i = MyGenericClass<MyClass>()
i.foo(with: MySubclass())
i.bar(with: MySubclass())

let j = MyGenericClass<MyClass & MyProtocol>()
j.foo(with: MySubclass())
j.bar(with: MySubclass()) // error
j.baz(with: MySubclass()) // error