Open Radar

 
Summary:
I’d like Swift to allow me to explicitly specialize generic functions, allowing me to write functions which use the generic type only in their return value.

Steps to Reproduce:
I have two example, one small which demonstrates the problem but is a bit non-sensical:

extension Int {
	func cast<T>() -> T { return self as! T }
}

let value = 5
let casted = 5.cast<Double>()

And one more complex that demonstrates what I’m actually trying to achieve in a project:

class ObjectBundle<T: NSObject> {
	var objects: [String:T] = [:]
	
	func add(object: T) {
		self.objects[NSStringFromClass(object.dynamicType)] = object
	}
	
	func get<U: NSObject>() -> U? {
		return self.objects[NSStringFromClass(U.self)]
	}
}

class MyBaseClass: NSObject {
	var myBaseProp: Int = 0
}
class MyClass: MyBaseClass {
	var myProp: Int = 0
}

var bundle = ObjectBundle<MyBaseClass>()
bundle.add(MyBaseClass())
bundle.add(MyClass())
let obj = bundle.get<MyClass>()