Swift: debugDescription excluding some fields

gistfile1.txt

extension CustomDebugStringConvertible {
    public func debugDescription(excluding fields: [String]) -> String {
        let excluded = Set<String>(fields)
        let m = Mirror(reflecting: self)
        let arguments = m.children
            .filter { child in
                return (child.label == nil) || !excluded.contains(child.label!)
            }
            .map { c -> String in
                let value = (type(of: c.value) == String.self) ? "\"\(c.value)\"" : "\(c.value)"
                if let label = c.label {
                    return "\(label): \(value)"
                }
                else {
                    return "\(value)"
                }
            }
            .joined(separator: ", ")
        let debugDescription = "\(m.subjectType)(\(arguments))"
        return debugDescription
    }
}