Swift - Storing Collections of Data Using Array(slicing or indexing with negative indices(Array extension))

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)

Practical Programming: An Introduction to Computer Science Using Python 3 (Pragmatic Programmers) (Paul Gries (著)、Jennifer Campbell (著)、Jason Montojo (著)、Lynn Beighley (編集)、Pragmatic Bookshelf)のChapter 8(Storing Collections of Data Using Array)、8.9(Exercises) 2.をSwiftで考えてみる。

8.9(Exercises) 2.

コード(Xcode)

array.swift

//
//  array.swift
//  array
//
//  Created by kamimura on 8/21/14.
//  Copyright (c) 2014 kamimura. All rights reserved.
//

import Foundation

extension Array {
    func indexAt(i:Int) -> T {
        if i >= 0 {
            return self[i]
        }
        let new_index:Int = self.count + i
        return self[new_index]
    }
    func slice(start:Int = 0, end:Int? = nil) -> Array {
        var new_start = start >= 0 ? start : self.count + start
        var new_end:Int
        if end == nil {
            new_end = self.count
        } else if end! >= 0 {
            new_end = end!
        } else {
            new_end = self.count + end!
        }
        var result:Array = []
        if new_start >= new_end {
            return []
        }
        for i in new_start..<new_end {
            result.append(self[i])
        }
        return result
    }
}

main.swift

//
//  main.swift
//  sample2
//
//  Created by kamimura on 8/21/14.
//  Copyright (c) 2014 kamimura. All rights reserved.
//

import Foundation

let kingdoms:[String] = ["Bacteria", "Protozoa", "Chromista", "Plantae", "Fungi", "Animalia"]

println(kingdoms.indexAt(-6))

println(kingdoms.indexAt(-1))

println(kingdoms.slice(start: -6, end: -3))

println(kingdoms.slice(start: -4, end: -1))

println(kingdoms.slice(start: -2))

println(kingdoms.slice(start: -1, end: -2))

入出力結果(Console Output)

Bacteria
Animalia
[Bacteria, Protozoa, Chromista]
[Chromista, Plantae, Fungi]
[Fungi, Animalia]
[]
Program ended with exit code: 0