How to check if option exists?

[ZedZipDev]

Is it possible to check if this option passed by user or it is only the default value?

[ericnewton76]

I don't believe so. An implementation redesign could hold that as a list of options and values that were set by the library to determine.

A better way to determine via your own implementation is to keep a record of property setter calls on your Options type: (psuedo code, so excuse syntax errors)

public class MyOptions 
{
    private string _MyOption1 = "some_default_value";
    [Option("MyOption1")]
    public string MyOption1 
    { 
        get => _MyOption1;
        set {
            _SetValues[nameof(MyOption1)] = value;
            _MyOption1 = value;
        }

    private Dictionary<string,string> _SetValues = new Dictionary<string,string>();
    public IDictionary<string,string> GetSetValues() => _SetValues;
}

Now you'll know if the library set the value or if it was never set, thus staying as the default:

> myprogram --MyOption1 some_default_value

[Brice-xCIT]

Unless I missed a configuration gotcha, @ericnewton76's solution does not seem to work anymore with 2.6.0. Properties are always set to their default value even if the Option was not present in the arguments.

[moh-hassan]

@Brice-xCIT

Properties are always set to their default value even if the Option was not present in the arguments.

Properties are set to default(T) See Default values table

For Nullable<T> it's set to null.

Value is overwritten by Default Property of OptionAttribute if it's set.

        [Option(Default=123)]
        public int Size { get; set; } //Size will be 123 if the Option was not present in the arguments

[Brice-xCIT]

Hi @moh-hassan, I understand your point, however the issue is not to give an option a default value, but to identify if an option was set by the user or not. In other words, was the option populated with a default, or was it populated with the user input? There could be different ways of doing that but currently the library offers none.

[moh-hassan]

@Brice-xCIT
You can use Unparser Extension method FormatCommandLine with the new feature in v2.7 SkipDefault to know if the option is populated with a default or set by user.
The following Extension method IsSetByUser is used to check the option status.

  static class Ex
{
  // return true if option is set by user otherwise it return false;
  public static bool IsSetByUser<T>(this T options, string option)
  {
  //unparse options
  	string args = CommandLine.Parser.Default.FormatCommandLine(options, config => config.SkipDefault = true);
	 Console.WriteLine($"Unparser:  {args}");   
	 var status =args.Contains(option);
	 if (status)
	 {
		 Console.WriteLine($"option: {option} is Set by user");
		 return true;
	 }
	 Console.WriteLine("option: {option} is Set by Parser");	
	return false;
  }
}  

[Brice-xCIT]

Hi @moh-hassan, thank you for pointing out to this new feature, it looks promising. However if the user did pass a value that was also the default value, this method will not detect it. I'm thinking now maybe the best solution is to just use Nullable<> on properties that need to be tracked for user customization.