CommandLineOptions with DynamicMemberLookup

CommandLineOptions.swift

extension CommandLine {
  
  @dynamicMemberLookup
  public struct Options {
    private let dict: [String : String]
    public init?(_ arguments: [String]) {
      let keysWithValues = arguments.dropFirst().compactMap(parse)
      if keysWithValues.isEmpty { return nil }
      self.dict = Dictionary(keysWithValues) { $1 }
    }
    
    public subscript(dynamicMember member: String) -> String? {
      return dict[member]
    }
  }
  
  static var options: Options? { return Options(arguments) }
  
  static func parse(argument: String) -> (String, String)? {
    let splits = argument.split(separator: "=", maxSplits: 2)
    
    guard splits.count > 1 else { return nil }
    
    let name = String(splits[0].dropFirst()).lowercased()
    
    if name.isEmpty { return nil }
    
    let value = String(splits[1])
    
    return (name, value)
  }
}

if let options = CommandLine.options,
  let username = options.user
{
  print(username)
}