Re: [review][JSON] Some thoughts on recent reviews

From: Peter Dimov (pdimov_at_[hidden])
Date: 2020-09-23 13:21:01

Niall Douglas wrote:

> For the record, I've had offlist email discussions about proposed 
> Boost.JSON with a number of people where the general feeling was that 
> there was no point in submitting a review, as negative review feedback 
> would be ignored, possibly with personal retribution thereafter, and the 
> library was always going to be accepted in any case.

Personal retribution, really?

> Consider this: a Hana Dusíková type all-constexpr JSON parser could let 
> you specify to the compiler at compile time "this is the exact structure 
> of the JSON that shall be parsed". The compiler then bangs out optimum 
> parse code for that specific JSON structure input. At runtime, the parser 
> tries the pregenerated canned parsers first, if none match, then it falls 
> back to runtime parsing.

That's definitely an interesting research project, but our ability to 
imagine it does not mean that people have no need for what's being 
submitted - a library with the speed of RapidJSON and the usability of JSON 
for Modern C++, with some additional and unique features such as incremental 
parsing.

To go on your tangent, I, personally, think that compile-time parsing is 
overrated because it's cool. Yes, CTRE is a remarkable accomplishment, and 
yes, Tim Shen, the author of libstdc++'s <regex> also thinks that 
compile-time regex parsing is the cure for <regex>'s ills. But I don't think 
so. In my unsubstantiated opinion, runtime parsing can match CTRE's 
performance, and the only reason current engines don't is because they are 
severely underoptimized.

Similarly, I doubt that a constexpr JSON parser will even match simdjson, 
let alone beat it.