std.json API improvement - Request for code review

[Sean Kelly]

Robert Jacques Wrote:

> On Mon, 13 Sep 2010 14:30:10 -0400, Sean Kelly <sean at invisibleduck.org>  
> wrote:
> 
> >
> > Could all this sit atop a SAX-style API?  I'm not likely to ever use an  
> > API that requires memory allocation for parsing or writing data.
> 
> Well, writing data could be done using output ranges easily enough, so no  
> extra memory writing troubles there. As for parsing, the biggest cost with  
> JSON is that fact that all strings can include escape chars, so things  
> have to be copied instead of sliced.

What I've always done is to not automatically unescape string data but rather provide a function for the user to do it so they can provide the buffer.  Alternately, this behavior could be configurable.  Escaping output should definitely be configurable though.  In fact, I often don't even want numbers to be automatically converted from their string to real/int representation, since it's common for me to want to operate on the value as a string.  So even this I like being given the original representation and calling to!int or whatever on my own.

> However, there's nothing preventing a  
> SAX style implementation in the format itself. Except that JSON has less  
> extra meta-data than XML so SAX becomes a less informative. Instead of:
> 
> object start vector
> member x
> number 42.8
> object end vector
> 
> you have something like
> 
> object start
> member vector
> object start
> member x
> number 42.8
> object end
> object end
> 
> For myself, the files are under a mb and random access makes everything  
> much faster to program and debug.

Random access is definitely nice, it's more the performance cost of all those allocations that's an issue for me.  What I'm basically looking for is a set of events like this:

alias void delegate(char[]) ParseEvent;
ParseEvent onObjectEnter, onObjectKey, onObjectLeave;
ParseEvent onArrayEnter, onArrayLeave;
ParseEvent onStringValue, onFloatValue, onIntValue;
ParseEvent onTrueValue, onFalseValue, onNullValue;

With corresponding write events on the output side so if I hooked the parser to the writer the data would all flow through and generate output identical to the input, formatting notwithstanding (though I'd add the option to write numbers as either a string, real, or int).  I like the event parameter being a char[] because it allows me to unescape string data in place, etc.

There are some advanced-mode writer options I'd like as well, like the ability to dump a char[] blob directly into the destination string without translation, saving and restoring writer state, etc.

I don't know if anyone besides myself would find all this useful though.  These are just some things I've found necessary for the work I do.