SwiftでMethod Swizzling ref: http://qiita.com/morizotter/items/a6dffb547675e9184326

Anyfile.swift

func swizzle() {
    var dict = ["This is Key.": "This is value."] as NSDictionary
    var method: Method = class_getInstanceMethod(object_getClass(dict), "description")
    var swizzledMethod: Method = class_getInstanceMethod(object_getClass(dict), "myDescription")
    method_exchangeImplementations(method, swizzledMethod)

    println(dict.description)
}

console

MY DESCRIPTION!!
{
    "This is Key." = "This is value.";
}

NSDictionary.swift

extension NSDictionary {
    func myDescription() -> String {
        println("MY DESCRIPTION!!")
        return myDescription()
    }
}