Swift4Swizzling.swift

import Foundation
import ObjectiveC.runtime

@objc class Dummy: NSObject {
    @objc dynamic func methodA() { print("methodA") }
    @objc dynamic func methodB() { print("methodB") }
    @objc func methodC() { print("methodC") }
    @objc func methodD() { print("methodD") }
}

var dummy = Dummy()
let selectorA = #selector(Dummy.methodA)
let selectorB = #selector(Dummy.methodB)
let selectorC = #selector(Dummy.methodC)
let selectorD = #selector(Dummy.methodD)
let methodA = class_getInstanceMethod(Dummy.self, selectorA)
let methodB = class_getInstanceMethod(Dummy.self, selectorB)
let methodC = class_getInstanceMethod(Dummy.self, selectorC)
let methodD = class_getInstanceMethod(Dummy.self, selectorD)
method_exchangeImplementations(methodA!, methodB!)
method_exchangeImplementations(methodC!, methodD!)
dummy.methodA()             // Prints methodB
dummy.methodB()             // Prints methodA
dummy.perform(selectorA)    // Prints methodB
dummy.perform(selectorB)    // Prints methodA
dummy.methodC()             // Prints methodC
dummy.methodD()             // Prints methodD
dummy.perform(selectorC)    // Prints methodD
dummy.perform(selectorD)    // Prints methodC