Charles Wilson's Blog

This is my third post on the Swift command line. In the first, I wrote on how to do command line input with Swift. In the second, I cleaned up the code after a year of tinkering with Swift. In this third installment, I get rid of more Objective-C.

Almost a month ago, Apple released Swift into the open source community. Pretty spiffy that. So, being the language wonk that I am, I bopped over to the Swift site and downloaded the sources. After a bit of scrounging, I discovered that there existed a standard library call to read a line from the input stream. I was a bit disappointed that I’d not seen this talked about anywhere, but that’s life.

So, I’ve updated my code sample and present it below. I do some forced unwrapping as the point is to highlight the process. Be sure to code defensively.

I’ll probably come back to this one more time once I’ve had a chance to look more into the Swift standard library so I can eliminate my untidy Objective-C dependent putString() routine.

//
//  swift_intput_routines.swift
//
//  Created by Charles Wilson on 9/27/2014.
//  Revised by Charles Wilson on 9/27/2015.
//  Revised by Charles Wilson on 12/21/2015.
//
//  Copyright (c) 2014 – 2015 Charles Wilson. All rights reserved.
//
//  Permission is granted to use and modify so long as attribution is made.
//

import Foundation

func putString (outputString : String = “”)
{
if !outputString.isEmpty
{
NSFileHandle.fileHandleWithStandardOutput().writeData((outputString as NSString).dataUsingEncoding(NSUTF8StringEncoding)!)
}
}

func getString (prompt : String = “”) -> String?
{
if !prompt.isEmpty
{
putString(prompt)
}

return readLine(stripNewline: true)
}

func getCharacter () -> Character
{
let inputValue     : UInt32      = UInt32(getchar())
var inputCharacter : Character

inputCharacter = Character(UnicodeScalar(inputValue))

return inputCharacter
}

func getInteger (prompt : String = “”) -> Int
{
if !prompt.isEmpty
{
putString(prompt)
}

return (getString()! as NSString).integerValue
}

func getFloat (prompt : String = “”) -> Float
{
if !prompt.isEmpty
{
putString(prompt)
}

return (getString()! as NSString).floatValue
}

Here’s the main to exercise it.

//
//  main.swift
//
//  Created by Charles Wilson on 9/27/2014.
//  Revised by Charles Wilson on 9/27/2015.
//  Revised by Charles Wilson on 12/21/2015.
//
//  Copyright (c) 2014 - 2015 Charles Wilson. All rights reserved.
//
//  Permission is granted to use and modify so long as attribution is made.
//

import Foundation

var name = getString("What is your name? ")!

if name.isEmpty
{
    name = "George"
    
    putString("That's not much of a name. I'll call you '\(name)'\n")
}
else
{
    putString("Your name is '\(name)'\n")
}

let age = getInteger("How old are you \(name)? ")

putString("You are \(age) years old\n")

// get a value without a prompt
let number = getInteger()

putString("\(number) is a nice number\n")

let floating = getFloat("Enter a floating point number: ")

putString("\(floating) works for me\n")

var c : Character

putString("Type stuff. Enter ^ when done.\n")

let sentinel : Character = Character(UnicodeScalar("^"))
var in_c     : Character

repeat
{
    in_c = getCharacter()
}
while ( in_c != sentinel )

putString("\n\n")
putString("bye\n")