iPhone app, a new born language, it may good but the IDE, xcode is bad compare with Visual Studio. It just like a baby. playground can only use without connect to other library...you can not do a simply refactor of renaming a variable. You can go to definition and find reference, but you can not go to implementation....I should write them on xcode not here basically it is not the fault of swift, but it tightly to it, unless you want to use a notepad to write it. Swift