Swift - Liberated functions: First Class Functions(declarations, expressions(Closures), order, Optional, nil)

The Swift Programming Language
Apple Inc.

開発環境

• OS X Mavericks - Apple(OS)
• Xcode 6.0 Beta
• Swift (プログラミング言語)

Head First JavaScript Programming (Eric T. Freeman (著)、 Elisabeth Robson (著)、 O'Reilly Media )のChapter 10(Liberated functions: First Class Functions)、BE THE BROWSER(p.438)をSwiftで考えてみる。

BE THE BROWSER(p.438)

コード(Xcode)

main.swift

//
//  main.swift
//  sample438
//
//  Created by kamimura on 9/7/14.
//  Copyright (c) 2014 kamimura. All rights reserved.
//

import Foundation

let midi:Bool = true
var midiInterface:() -> ()
var midiInterfaceOptional:(() -> ())?
var midiInterfaceOptional1:(() -> ())?


// play() Use of unresolved identifier 'play'
func play() {
    println("play")
}
play()

// myPause() Use of unresolved identifier 'myPause'
let myPause = {() in println("pause")}
myPause()

// stop() Use of unresolved identifier 'stop'
func stop() {
    println("stop")
}
stop()

// createMidi() Use of unresolved identifier 'createMidi'
func createMidi() {
    println("createMidi")
}
createMidi()

// midiInterface() Variable 'midiInterface' used before being initialized
if midi {
    midiInterface = {() in println("midiInterface")}
    midiInterface()
}
// midiInterface() Variable 'midiInterface' used before being initialized

println("Optional")
println("before")
midiInterfaceOptional?()
if midi {
    println("if")
    midiInterfaceOptional = {() in println("midiInterfaceOptional")}
    midiInterfaceOptional?()
}
println("after")
midiInterfaceOptional?()

println("before1")
if !midi {
    println("if1")
    midiInterfaceOptional1 = {() in println("midiInterfaceOptional1")}
    midiInterfaceOptional1?()
}
println("after1")
midiInterfaceOptional1?()

入出力結果(Console Output)

play
pause
stop
createMidi
midiInterface
Optional
before
if
midiInterfaceOptional
after
midiInterfaceOptional
before1
after1
Program ended with exit code: 0