Many languages have libraries built in that do something reasonable with JSON. Usually you just make a class or struct, instantiate it, and then generate JSON, no need to have a separate compile step. When going the other direction, I usually just format the JSON, copy that into my code, then fix the compile errors.
XML has all that tooling because it needs it. JSON is a lot more straightforward, is more compact, and is faster to parse and (probably) generate.
If you're going to go through the effort of a compile step, you should probably just use a binary protocol, which will get you even better performance and getting documentation out of the box (e.g. protocol buffers schemas are very readable).
I see absolutely no reason to use XML these days as a data format, but it's still a response choice as a markup format (you know, what the M stands for).
> Many languages have libraries built in that do something reasonable with JSON.
What about cross-language? In C# I define a class containing a `DateTime` field, export the schema with xsd, and generate classes for Java with xjc, and get back a field of (an equivalent of) `DateTime` type. Doing what you suggest with JSON, I'd get a "string". Thanks but no thanks.
> If you're going to go through the effort of a compile step, you should probably just use a binary protocol, […] I see absolutely no reason to use XML these days as a data format,
In our product we use a relational db (SQLServer) combined with XML. Each table has a structured part which is put into relational columns, plus an extensions part that is put into a "Data" XML column for semi-structured data. SQLServer supports XQuery so we can query the semi-structured data from SQL when needed.
This wouldn't fly with a binary format.
EDIT: yes, SQLServer also supports JSON, but has special optimizations for XML (e.g., it can understand schema types, it supports XML indexes which "shred" XML to a more efficient binary representation based on schema, etc.)
XML has all that tooling because it needs it. JSON is a lot more straightforward, is more compact, and is faster to parse and (probably) generate.
If you're going to go through the effort of a compile step, you should probably just use a binary protocol, which will get you even better performance and getting documentation out of the box (e.g. protocol buffers schemas are very readable).
I see absolutely no reason to use XML these days as a data format, but it's still a response choice as a markup format (you know, what the M stands for).