CODEWITHSUNDEEP
iosswiftgenericsprotocols
eunoia
eunoia

Reputation: 246

Swift Protocol Function Overloading

Is it possible to overload a protocol function and have the correct definition be called when dealing directly with the protocol type?

Here's some code to illustrate the issue

protocol SomeProtocol {
    func doSomething<T>(obj: T)
}

class SomeClass : SomeProtocol {
    func doSomething<T>(obj: T) {
        print("Generic Method")
    }
    func doSomething(obj: String) {
        print(obj)
    }
}

let testClass = SomeClass()

testClass.doSomething("I will use the string specific method")
(testClass as SomeProtocol).doSomething("But I will use the generic method")

Edit: To clarify, the code works. I want to know why both calls do not use the string specific method.

Double Edit: Removed the intermediary dispatch class for a simpler example

Is this a bug, current limitation, or intended functionality? If this is intended, can someone please explain why?

Swift 2.0, Xcode 7.0

Answer

You can't overload a protocol function and expect the correct definition to be called. This is because the definition to call is picked at compile time. Since the compiler doesn't know the concrete type, it chooses the only definition known at compile time, doSomething<T>.

Upvotes: 4

Views: 1688

Answers (1)

Chuy47
Chuy47

Reputation: 2417

I tested your code here http://swiftstub.com/ and it worked fine. First it prints "I will use the specific method" and then "Generic Method":

I will use the specific methodGeneric Method

Upvotes: 1

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