配列の一部範囲を取り出して新しい配列を生成する方法のパフォーマンス比較 ref: http://qiita.com/lovee/items/155a662146445ca4a79c

file0.swift

let array = [Int](0 ..< 10000)
let number = array[1000] // number = 1000

file1.swift

let array = [Int](0 ..< 10000)
let slice = array[1000 ..< 2000] // slice = [1000, 1001, 1002, ..., 1999]

file2.swift

let array = [Int](0 ..< 10000)
let newArray = Array(array[1000 ..< 2000]) // newArray = [1000, 1001, 1002, ..., 1999]

file3.swift

let array = [Int](0 ..< 10000)
let range = 4000 ..< 5000
let newArray = range.map { (i) -> Int in
    return array[i]
}

file4.swift

let array = [Int](0 ..< 10000)
let range = 4000 ..< 5000
let newArray = Array(array[range])

file5.swift

var baseArray = [Int](0 ..< 10000)
let childArray1Range = 3000 ..< 3050
let childArray2Range = 7000 ..< 7100

baseArray = baseArray.map { (i) -> Int in
    return i * i
}

let start1 = NSDate()
for _ in 0 ..< 10000 {
    let childArray1 = childArray1Range.map { (i) -> Int in
        return baseArray[i]
    }
    let childArray2 = childArray2Range.map { (i) -> Int in
        return baseArray[i]
    }
}
print(-start1.timeIntervalSinceNow)

let start2 = NSDate()
for _ in 0 ..< 10000 {
    let childArray1 = Array(baseArray[childArray1Range])
    let childArray2 = Array(baseArray[childArray2Range])
}
print(-start2.timeIntervalSinceNow)

file6.swift

let queue = dispatch_queue_create("data", DISPATCH_QUEUE_SERIAL)
var baseArray = [Int](0 ..< 10000)
let childArray1Range = 3000 ..< 3050
let childArray2Range = 7000 ..< 7100

dispatch_sync(queue) { () -> Void in
    baseArray = baseArray.map { (i) -> Int in
        return i * i
    }
}

func getElement(i: Int) -> Int {
    var result = 0
    dispatch_sync(queue) { () -> Void in
        result = baseArray[i]
    }
    return result
}

func getElements(range: Range<Int>) -> [Int] {
    var result = [Int](range)
    dispatch_sync(queue) { () -> Void in
        result = Array(baseArray[range])
    }
    return result
}

let start1 = NSDate()
for _ in 0 ..< 10000 {
    let childArray1 = childArray1Range.map { (i) -> Int in
        return baseArray[i]
    }
    let childArray2 = childArray2Range.map { (i) -> Int in
        return baseArray[i]
    }
}
print(-start1.timeIntervalSinceNow)

let start2 = NSDate()
for _ in 0 ..< 10000 {
    let childArray1 = Array(baseArray[childArray1Range])
    let childArray2 = Array(baseArray[childArray2Range])
}
print(-start2.timeIntervalSinceNow)

let start3 = NSDate()
for _ in 0 ..< 10000 {
    let childArray1 = childArray1Range.map { (i) -> Int in
        return getElement(i)
    }
    let childArray2 = childArray2Range.map { (i) -> Int in
        return getElement(i)
    }
}
print(-start3.timeIntervalSinceNow)

let start4 = NSDate()
for _ in 0 ..< 10000 {
    let childArray1 = getElements(childArray1Range)
    let childArray2 = getElements(childArray2Range)
}
print(-start4.timeIntervalSinceNow)