Performance of std.json

[Chris Williams via Digitalmars-d]

On Monday, 2 June 2014 at 00:39:48 UTC, Jonathan M Davis via 
Digitalmars-d wrote:
> I know that vibe.d uses its own json implementation, but I 
> don't know
> how much of that is part of its public API and how much of that 
> is
> simply used internally: http://vibed.org

In general, I've been pretty happy with vibe.d, and I've heard 
that the parser speed of the JSON implementation is good. But I 
must admit that I found the API to be fairly obtuse. In order to 
do much of anything, you really need to serialize/deserialize 
from structs. The JSON objects themselves are pretty impossible 
to modify.

I haven't looked at how vibe's parser works, but any very-fast 
parser would probably need to support an input stream, so that it 
can build out data in parallel to I/O, and do a lot of manual 
memory management. E.g. you probably want a stack of reusable 
node buffers that you use to add elements to as you scan the JSON 
tree, then clone off purpose-sized nodes from the work buffers 
when you encounter the end of the definition. Whereas, the 
current implementation in std.json only accepts a complete string 
and for each node starts with no memory and has to 
allocate/reallocate for every fresh piece of information.

Having worked with JSON libraries quite a bit, the key to a good 
one is the ability to refer to paths through the data. So besides 
the JSON objects themselves, you need something like a "struct 
JPath" that represents an array of strings and size_ts, which you 
can pass into get, set, has, and count methods. I'd view the lack 
of that as the larger issue with the current JSON implementations.