Camel case to snake case in Swift

SnakeCase.swift

extension String {
  
  func snakeCased() -> String? {
    let pattern = "([a-z0-9])([A-Z])"

    let regex = try? NSRegularExpression(pattern: pattern, options: [])
    let range = NSRange(location: 0, length: count)
    return regex?.stringByReplacingMatches(in: self, options: [], range: range, withTemplate: "$1_$2").lowercased()
  }
}

just use fileprivate extension