acrosa/gist:fd1e5aeeccafeb1d1a6b

NachoSoto · 2014-12-06T00:09:20Z

Remember my example:

class SomeClassA: ParentClass, ClassProtocol {}
class SomeClassB: ParentClass, ClassProtocol {}

I can make ClassA and ClassB inherit from the more specific CustomClassAndProtocol, but I want to avoid that. Maybe ClassB will inherit from ParentClassSubclass (a subclass of ParentClass, for example.

Of course I can solve this by restricting each of the classes, but I want to avoid solving this with inheritance.

StanTwinB · 2014-12-06T00:33:35Z

Another example in UIInputViewController.h

@property (nonatomic, readonly) NSObject <UITextDocumentProxy> *textDocumentProxy;

is compiled to Swift as

var textDocumentProxy: NSObject { get }

If the complier can't do it, I don't think we can

drodriguez · 2014-12-06T01:11:07Z

Best I can do:

protocol TestProtocol {
}

class ParentClass {
}

class TestClassA : ParentClass, TestProtocol {
}

class TestClassB : ParentClass, TestProtocol {
}

class TestClassC : ParentClass {
}

class TestClassD : TestProtocol {
}

struct Test<T where T: ParentClass, T: TestProtocol> {
  var a: T.Type {
    get {
      return T.self
    }
  }
}

let t1 = Test<TestClassA>()
let t2 = Test<TestClassB>()
let t3 = Test<TestClassC>() // Type 'TestClassC' does not conform to protocol 'TestProtocol'
let t4 = Test<TestClassD>() // Type 'TestClassD' does not inherit from 'ParentClass'

If you can, I will use a little protocol helper and call it a day:

protocol ParentClassProtocol {
}

class ParentClass: ParentClassProtocol {
}

struct Test2 {
  var b: protocol<ParentClassProtocol, TestProtocol>.Protocol {
    get {
      return TestClassA.self
    }
  }
}

You can add this protocol (a tag) in an extension for classes like UIView if you need.

The truth is that protocol<> should actually be type<> and work for real types...

	protocol ClassProtocol
	{
	var property: SomePropertyProtocol? { get set }
	}

	protocol SomePropertyProtocol
	{
	}

	class SomeClass : ClassProtocol
	{
	var property: SomePropertyProtocol?
	}

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NachoSoto commented Dec 6, 2014

Uh oh!

StanTwinB commented Dec 6, 2014

Uh oh!

drodriguez commented Dec 6, 2014

Uh oh!