Swift extension for string manipulation

string.swift

//
//  String 1.0
//  Created by Caleb Hess on 2/22/16.
//

public extension String {

    public var count: Int { 
        return self.characters.count 
    }
    
    public var asURL: NSURL? { 
        return NSURL(string: self) 
    }
    
    public subscript (i: Int) -> String {
        return String(self[i] as Character)
    }
    
    public subscript (r: Range<Int>) -> String {
        return substringWithRange(Range(start: startIndex.advancedBy(r.startIndex), end: startIndex.advancedBy(r.endIndex)))
    }
    
    public func split(sepearator: String) -> [String] {
        return self.componentsSeparatedByString(sepearator)
    }
    
    public func trim() -> String {
        return self.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())
    }
    
    public func replace(target: String, with: String) -> String {
        return self.stringByReplacingOccurrencesOfString(target, withString: with)
    }
    
    public func replace(values: [String:String]) -> String {
        var result = self
        
        for (target, with) in values {
            result = result.replace(target, with: with)
        }
        
        return result
    }
    
    public func indexOf(target: String) -> Int {
        if let range = self.rangeOfString(target) {
            return self.startIndex.distanceTo(range.startIndex)
        } else {
            return -1
        }
    }
    
    public func contains(target: String) -> Bool {
        return self.indexOf(target) != -1
    }
}

// --------------------
// examples of use
let str = "hello world"
str.count                                       // 11
str[1]                                          // "e" 
str[1...3]                                      // "ell" 
str.split(" ")                                  // ["hello", "world"] 
str.trim()                                      // "hello world"
str.replace("h", with: "j")                     // "jello world"
str.replace(["h": "j", "world": "land"])        // "jello land"
str.indexOf("world")                            // 6
str.contains("jupiter")                         // false
"https://example.com".asURL                     // NSURL?