Here's a thought: what about always storing JSON numbers as strings (albeit tagged with the "number" type, to differentiate them from actual strings in the input), and the user specifies what type to convert it to? The default type can be something handy, like int, but the user has the option to ask for size_t, or double, or even BigInt if they want (IIRC, the BigInt ctor can initialize an instance from a digit string, so if we adopt the convention that non-built-in number-like types can be initialized from digit strings, then std.json can simply take a template parameter for the output type, and hand it the digit string. This way, we can get rid of the std.bigint dependency, except where the user actually wants to use BigInt.)
Some JSON files can be quite large...
For example, I have a compressed 175 Gig of Reddit comments (one file per month) I would like to work with using D, and time + memory demands = money.
Wouldn't it be a pain not to store numbers directly when parsing in those cases (if I understood you correctly)?
