Support event driven parsing.

[canatella]

This pull requests adds "SAX" like event driven parsing to json11. When parsing lots of objects, it allows having access to them without waiting for the whole parsing to finish. It should also limit memory usage.

This is a tentative request, it still needs work but I wanted to know if you would be open to such a feature and how you would envision it. I still need to

• write tests,
• avoid keeping all data in memory.

Also I'm not an expert in C++ so do not hesitate to point me to the problems in my code.

[smarx]

Automated message from Dropbox CLA bot

@canatella, thanks for the pull request! It looks like you haven't yet signed the Dropbox CLA. Please sign it here.

[artwyman]

Hi @canatella. Trying to get caught up on PR's during the holiday lull.
I'm not opposed to supporting event-based parsing in theory (though I wonder if @j4cbo has thoughts as primary author). The current strategy of mixing it into the standard parser does seem not to get most of the benefit, due to keeping everything in memory as you mention. In most cases there wouldn't really be a benefit to using the events, vs. finishing the parse and then examining the resulting object. You could get earlier results on a streaming parse, but that should only be relevant for long streams, in which case the memory size would be an issue. My guess is that if you wanted the full benefit of this style of parser, you'd want it to be the primary parse mechanism, then have the "standard" parse be built as an event handler.

[artwyman]

See comments above, but I'm going to use the code-review flow for this.