Swift utility class for regular expression

Regexp.swift

import Foundation

class Regexp {
    let internalRegexp: NSRegularExpression
    let pattern: String
    
    init(_ pattern: String) {
        self.pattern = pattern
        do {
            self.internalRegexp = try NSRegularExpression(pattern: pattern, options: NSRegularExpressionOptions.CaseInsensitive)
        } catch let error as NSError {
            print(error.localizedDescription)
            self.internalRegexp = NSRegularExpression()
        }
    }
    
    func isMatch(input: String) -> Bool {
        let matches = self.internalRegexp.matchesInString( input, options: [], range:NSMakeRange(0, input.characters.count) )
        return matches.count > 0
    }
    
    func matches(input: String) -> [String]? {
        if self.isMatch(input) {
            let matches = self.internalRegexp.matchesInString( input, options: [], range:NSMakeRange(0, input.characters.count) )
            var results: [String] = []
            for i in 0 ..< matches.count {
                results.append( (input as NSString).substringWithRange(matches[i].range) )
            }
            return results
        }
        return nil
    }
    
    func replace(string: String, replaceString: String) -> String? {
        let matchs = self.internalRegexp.stringByReplacingMatchesInString(string, options: [], range: NSMakeRange(0, string.characters.count), withTemplate: replaceString)
        return matchs
    }
}

Add func replace