Matcher to find mustache placeholder keys and replacement ranges

MustacheRegex.swift

extension Array where Element == NSRange {
    func maxRange() -> Int {
        return self.reduce(0) { (prev, next) in
            let maxNext = NSMaxRange(next)
            return Swift.max(prev, maxNext)
        }
    }
}

extension String {
    
    private static let mustacheRegex = try! NSRegularExpression(pattern: #"\{\{?(?<mustache>(#[a-z])?[a-z]+.[a-z])*\}?\}"#, options: [])
    private static let mustacheKeyname = "mustache"
    
    func mustachePlaceholders() -> [(String, NSRange)] {
        var shouldStop = false
        var placeholders: [(keyname: String, replacementRange: NSRange)] = []
        var counterIndex: Int = 0
        while !shouldStop {
            guard counterIndex < self.count else { shouldStop = true; break }
            if let match = String.mustacheRegex.firstMatch(in: self, options: [], range: NSRange(counterIndex..<self.count)) {
                let range = match.range(withName: String.mustacheKeyname)
                if range.location != NSNotFound {
                    placeholders.append((keyname: NSString(string: self).substring(with: range), replacementRange: match.range))
                }
            } else { shouldStop = true; break }
            counterIndex = placeholders.map({ $0.replacementRange }).maxRange() + 1
        }
        return placeholders
    }
}