forwardInvocation.swift

// please... don't do this

import Foundation

class F: NSObject
{
    @objc func foo() {
        print("hi")
    }
}

class C: NSObject { }

func addMethod(c: AnyClass, _ sel: Selector, types: String, usingBlock block: @convention(block) (AnyObject, AnyObject) -> Unmanaged<AnyObject>!)
{
    types.withCString { (typeStr: UnsafePointer<Int8>) -> Void in
        class_addMethod(c, sel, imp_implementationWithBlock(unsafeBitCast(block, AnyObject.self)), typeStr)
        return
    }
}

addMethod(C.self, "methodSignatureForSelector:", types: "@@::") { receiver, arg -> Unmanaged<AnyObject>! in
    print("getting signature")
    return F().performSelector("methodSignatureForSelector:", withObject: arg as AnyObject!)
}

addMethod(C.self, "forwardInvocation:", types: "v@:@") { receiver, arg -> Unmanaged<AnyObject>! in
    print("forwarding")
    arg.performSelector("invokeWithTarget:", withObject: F())
    return nil
}

C().performSelector("foo") // prints "hi"