Swift smart quotes

smartquotes.swift

// Light-weight Swift smart quote implementation
// By Rob Hudson
// 5/11/2015

import UIKit

let text = "\"Would you tell me, please, which way I ought to go from here?\" " +
"That depends a good deal on where you want to get to,\" said the Cat. " +
"\"I don’t much care where-\" said Alice. " +
"Then it doesn’t matter which way you go,\" said the Cat. " +
"\"-so long as I get SOMEWHERE,\" Alice added as an explanation. " +
"Oh, you’re sure to do that,\" said the Cat, \"if you only walk long enough.\""

func useSmartQuotes(var string: String) -> String {
    string = replaceDumbQuote("'", string: string, leftQuote: "‘", rightQuote: "’")
    string = replaceDumbQuote("\"", string: string, leftQuote: "“", rightQuote: "”")
    
    return string
}

private func replaceDumbQuote(dumbQuote: Character, var #string: String, #leftQuote: String, #rightQuote: String) -> String {
    var characterSet = NSMutableCharacterSet.whitespaceAndNewlineCharacterSet()
    characterSet.addCharactersInString("([{:<=")
    
    while let characterIndex = find(string, dumbQuote) {
        let characterPosition = distance(string.startIndex, characterIndex)
        
        var prevChar: unichar
        if characterPosition != 0 {
            let prev = string[advance(characterIndex, -1)]
            prevChar = ("\(prev)" as NSString).characterAtIndex(0)
        } else {
            prevChar = (" " as NSString).characterAtIndex(0)
        }
        
        var smartQuote: String
        if characterSet.characterIsMember(prevChar) {
            smartQuote = leftQuote
        } else {
            smartQuote = rightQuote
        }
        let range = Range(start: advance(characterIndex, 0), end: advance(characterIndex, 1))
        string = string.stringByReplacingCharactersInRange(range, withString: smartQuote)
    }

    return string
}

useSmartQuotes(text)