String-Replacements.swift

var tempText = ":a/b?c,d=e&f"

var replacements = [
    (":","%3A"),
    ("/","%2F"),
    ("?","%3F"),
    (",","%2C"),
    ("=","%3D"),
    ("&","%26")]

extension String {
    func encode(replacements: [(String,String)]) -> String? {
        if let urlEncoded = stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet()) {
            return replacements.reduce(urlEncoded) {
                $0.stringByReplacingOccurrencesOfString($1.0, withString: $1.1)
            }
        }
        return .None
    }
}

tempText.encode(replacements)