Regular Expressions: How to replace patterns in Swift

RegExReplace.swift

// You need to import Foundation to use NSRegularExpression, NSError and NSString
import Foundation

/// This function takes three parameters
/// text: a string that we search in
/// pattern: a reqular expression pattern to use in the search
/// withTemplate: the string that we use instead of the occurrances we find in text
///
/// The method returns (text) with occurrance found using (pattern) replaced with (withTemplate)
func regexReplace(text:String, pattern:String, withTemplate:String) -> String {
    // Assign text to a local variable as text is immutable
    var _text = text
    
    // Create an NSError object to use with NSReqularExpression. Initialize with nil
    var error:NSError? = nil
    
    // Create an object of type NSRegularExpression. We'll call this objects methods to perform
    // RegEx operations, in this case, replacement. The object is initialized with three parameters
    // the (pattern) used in the search, (options) in this case we're using CaseInsensitive search
    // and (error) a pointer to an NSError object to assign errors to in case any errors happen.
    let regex = NSRegularExpression(pattern: pattern, options: .CaseInsensitive, error: &error)
    
    // We're calling stringByReplacingMatchesInString on the regex object. The method accepts four paramteres: 
    // the (text) to search in, (options) in this case, none, the (range) to search in, in the string and here we're searching
    // the whole string and finally (withTemplate) contains the value to be used.
    // In case we succeed, assign the updated text to _text variable.
    if let replacement = regex?.stringByReplacingMatchesInString(text, options: nil, range: NSMakeRange(0, countElements(text)), withTemplate: withTemplate) {
        _text = replacement
    } else {
        // If the error object is not nil print the error discrption.
        if((error) != nil) {
            print(error?.description)
        }
    }
    
    // return the final string
    return _text
}

Hi M-Medhat, very useful code, thank you for sharing. Do you have also a Swift 2 version?