How to replace a string with its uppercase with NSRegularExpression in Swift?

Question

I was trying to change hello_world to helloWorld by this snippet of code (Swift 3.0):

import Foundation

let oldLine = \"hello_worl         


        

Answer 1

One way to work with your case is subclassing NSRegularExpression and override replacementString(for:in:offset:template:) method.

class ToUpperRegex: NSRegularExpression {
    override func replacementString(for result: NSTextCheckingResult, in string: String, offset: Int, template templ: String) -> String {
        guard result.numberOfRanges > 2 else {
            return ""
        }
        let matchingString = (string as NSString).substring(with: result.rangeAt(2)) as String
        return matchingString.uppercased()
    }
}

let oldLine = "hello_world"
let fullRange = NSRange(0..helloWorld