Swift: check if generic type conforms to protocol

Question

I have a protocol that I defined like so:

protocol MyProtocol {
   ...
}

I also have a generic struct:

struct MyStruct <         


        

Answer 1

You need declare protocol as @objc:

@objc protocol MyProtocol {
    ...
} 

From Apple's "The Swift Programming Language" book:

You can check for protocol conformance only if your protocol is marked with the @objc attribute, as seen for the HasArea protocol above. This attribute indicates that the protocol should be exposed to Objective-C code and is described in Using Swift with Cocoa and Objective-C. Even if you are not interoperating with Objective-C, you need to mark your protocols with the @objc attribute if you want to be able to check for protocol conformance.

Note also that @objc protocols can be adopted only by classes, and not by structures or enumerations. If you mark your protocol as @objc in order to check for conformance, you will be able to apply that protocol only to class types.

Answer 2

A bit late but you can test if something responds to protocol with as ? test:

if let currentVC = myViewController as? MyCustomProtocol {
    // currentVC responds to the MyCustomProtocol protocol =]
}

EDIT: a bit shorter:

if let _ = self as? MyProtocol {
    // match
}

And using a guard:

guard let _ = self as? MyProtocol else {
    // doesn't match
    return
}