Substring of a string without taking into account of some characters

NSRangeExtension.swift

import Foundation 

extension NSRange {
    static func rangeOf(text: String, contains searchKey: String, with filterCharacters: [Character]?) -> NSRange {

        var filter = "[ ]{0,1}("
        filterCharacters?.forEach { filterCharacter in
            filter += "\\" + String(filterCharacter)
            if let lastCharacter = filterCharacters?.last, lastCharacter != filterCharacter {
                filter += "|"
            }
        }
        filter += "){0,1}[ ]{0,1}"

        var regex = ""
        searchKey.forEach { character in
            regex += "[" + String(character) + "]{1}"
            if let lastCharacter = searchKey.last, character != lastCharacter {
                regex += filter
            }
        }
        print(regex)
        return (text as NSString).range(of: regex, options: .regularExpression, range: NSRange(location: 0, length: text.length), locale: nil)
    }
}

let string = "MDX6"
let plate = "AM / DX6044"
let filter: [Character] = ["-", "/"]

let range = NSRange.rangeOf(text: plate, contains: string, with: filter)
print(range)