Add recommendations for option parsing

[springmeyer]

In C++ my experience says:

• If it is okay to use boost, use boost::program_options, it is a solid library.
• It is often not okay to use boost. The headers alone are > 50 MB 🙀 and contain > 13,000 files. And boost::program_options requires linking a precompiled library. This is massive weight and complexity for a build system just to parse options.
• So for lightweight C++ libs that might not otherwise have any dependencies we need to recommend a very lightweight option parsing solution.

/cc @GretaCB @joto @mapbox/core-tech @danpat

[springmeyer]

libraries to investigate:

• https://github.com/jarro2783/cxxopts
• http://optionparser.sourceforge.net/
• https://github.com/myint/optparse

[joto]

I usually just use getopt_long() available in libc for simpler cases. The interface is C and not C++ and slightly ugly. But for many cases this is simple enough and doesn't require an extra dependency. If this is not enough it is time to switch to boost::program_options anyway.

[joto]

Something to investigate: Clara "A simple to use, composable, command line parser for C++ 11 and beyond". By the same guy who created the Catch unit test framework.

[springmeyer]

Just learned from @kkaefer that mbgl is using https://github.com/Taywee/args for demo apps - which @brunoabinader brought in.

[springmeyer]

watching progress on Clara at mapbox/vtzero@70fc232. I'm in support for having Clara be our recommendation if @joto's experience is solid this week in this port.

[joto]

My experience with Clara so far:

Positive:

• Easy to use, clean code.
• Easy to integrate 42k header file.
• In active development.

Negative:

• Documentation is not complete.
• Still in development, changes to be expected.
• Single - char as parameter (often used to denote stdin) is not possible.

I think it is too early to recommend this as a standard tool, but I think collecting some experience with it is probably a good idea. (That's why I went ahead and used it in the relatively simple vtzero examples.)

[springmeyer]

I think collecting some experience with it is probably a good idea. (That's why I went ahead and used it in the relatively simple vtzero examples.)

👍 looking forward to learning more as you use it.