Allow omitting mandatory parameters

[masics]

If you have:
val configFile by parser.storing("--config", "-c", argName = "CONFIGFILE", help = "Configuration file") { asPath }
val version by parser.flagging("--version", help = "print version and exit")

You cannot specify only "--version" in command line - it will complain about "missing CONFIGFILE"

We need an option for allowing printing version.

Alternatively allow multiple configurations:
usage: --config CONFIGFILE
usage: --version

[xenomachina]

I've been working on a change to add "subcommand" support (see #2 ). Do you think that would be sufficient for what you're trying to do?

The user-interface would look slightly different. Instead of:

program --config CONFIGFILE
program --version

it would be:

program config CONFIGFILE
program version

In general, the format is:

program [global options...] SUB-COMMAND-NAME [sub-command-specific options and arguments]

This is similar to (and is based on) tools like git where one top-level command (git) has multiple sub-commands (checkout, clone, push, reset, etc.) that take different options/arguments.

[davidschreiber]

Sub-command support seems like the cleaner approach than omission of required parameters. I would really love to see this, as right now most of my commands are optional (although at least one should be probably mandatory at any time).

[joffrey-bion]

Sub-command support seems like the cleaner approach than omission of required parameters.

Subcommands are great, but I believe that it's not the right tool for the job here. Most programs don't work with subcommands and have instead some sort of "multiple usages" mindset, which I believe can be reasonably named the "anonymous subcommands" or "implicit subcommands" pattern.

I believe a lot of programs want usages like this:

Usage: program -h
Usage: program -v
Usage: program [standard args]

which corresponds to implicit "help", "version", and "default" subcommands.

There is actually one such implicit subcommand already implemented in kotlin-argparser: the help flag. It'd be nice to generalize this behaviour, maybe by using mutually exclusive option groups, that would act like anonymous subcommands.

A more simple implementation would be a special option type "standalone option" which would at least allow separating a single option from the rest, exactly like the help flag but for any custom option.

This feature would be very useful to implement for instance:

• a version flag
• a path to a configuration file that provides all mandatory arguments

[pcoltau]

Regarding the version flag, then I've recently made this PR: #70