Use compact valueName by default

[ddunbar]

By default, ArgumentParser currently uses a ArgumentHelp.valueName derived from the option name. While this is a nice standard default, I think it often leads to overly verbose --help text, and customizing with ArgumentHelp makes declaration a little verbose (super kudos for having it possible in v0.0.1 though!).

I think there is an argument to be made for having ArgumentParser use a default value name for well-known and common types, for example, using N for integral types.

One upside of this is that it helps communicate the expected type.

I can understand if this is perceived to be too much magic, though...

[natecook1000]

Something shorter would make for better defaults, especially with how long some property names can get. I like the idea of trying to select a value name that's appropriate for the type — we may even be able to hook into more information, like if you've indicated that the property is a file for autocomplete purposes (a la #1). What other default names would you expect beyond N for integers and something like value in the default case?

[ddunbar]

I'm not sure, very obvious ones to me are:

• <N>, for integral types
• <path>, for path types
• feels like there should be a good answer for float types, but nothing clearly sticks out <number> maybe? doesn't actually come up that much in command line tools so maybe not important
• I considered <str> or <string> for a string type, it does help to know the program thinks of it as a string, not sure I like the choice.

One thing I wondered was if it would make sense to actually make the ExpressibleByArgument be able to optionally provide this. So URL adopting could be <url>, for example.

@vlm any thoughts on this?

[vlm]

Yes, I'd love it to be something that can be set in the ExpressibleByArgument.

[rauhul]

Suppose we had a ExpressibleByArgument.defaultValueName to mirror ArgumentHelp.valueName... how would we know whether to the defaultValueName, valueName, or the argument's property name as the valueName?

[natecook1000]

ArgumentHelp.valueName is more local, so it would override anything from the protocol.

[rauhul]

So ArgumentHelp.valueName > ExpressibleByArgument.defaultValueName > @Arg/Opt/Flag name?