Dynamic defaults?

I have a generic method that is used in the Program.Main for some microservices. I want want to reuse options, but have different defaults.

Is there a way to specify the defaults that aren’t compiled (property attributes)?

[rmunn]

This could possibly be handled by having a DefaultFactory property in the Option and Value attributes. Functions can’t be attribute parameters, but you could make DefaultFactory be a string that could be the name of a method of your options class, e.g.:

[Option("foo", DefaultFactory=nameof(CalculateValue))]
string Foo { get; set; }

[Option("num")]
int Number { get; set; }

public string CalculateValue() {
    return (this.Number > 0) ? "positive" : (this.Number == 0) ? "zero" : "negative";
}

Then the Parser would first apply all default values specified by Default="some-constant-value", then for any DefaultFunc definitions it would use reflection to look up that name as a method on the options instance and call the method.

Wouldn’t be too hard to implement this, now that I think about it. @pauldotknopf - Would this idea fit your needs?

[rmunn]

Nope, can’t be done. By the time reflection is happening (at run-time), the nameof(Foo) expression found in the source code has been turned into the literal "Foo" at compile-time, and there is no way for any runtime code to tell whether it started as "Foo" or nameof(Foo). (You can try it yourself if you think I’m wrong). It will have to have a different name than Default. Possible names are DefaultFactory as I suggested, or DefaultProperty as suggested in https://github.com/commandlineparser/commandline/issues/191 for the HelpTextProperty. After reading that discussion, I’m leaning more towards DefaultProperty, because that gives more of a hint to the library user about what “shape” they should give it. (A “Factory” name should indicate that it should be a function that takes no parameters, but if you have a function then someone sometime is going to want to put parameters on it. Calling it FooProperty indicates that it should be a simple property with a get method, which can not (by definition) take parameters.)