std.data.json formal review

[H. S. Teoh via Digitalmars-d]

On Wed, Jul 29, 2015 at 03:22:05PM +0000, Don via Digitalmars-d wrote:
> On Tuesday, 28 July 2015 at 22:29:01 UTC, Walter Bright wrote:
[...]
> >The possible JSON values are:
> >    string
> >    number
> >    object (associative arrays)
> >    array
> >    true
> >    false
> >    null
> >
> >Since these are D builtin types, they can actually be a simple union
> >of D builtin types.
> 
> Related to this: it should not be importing std.bigint. Note that if
> std.bigint were fully implemented, it would be very heavyweight
> (optimal multiplication of enormous integers involves fast fourier
> transforms and all kinds of odd stuff, that's really bizarre to pull
> in if you're just parsing a trivial little JSON config file).
> 
> Although it is possible for JSON to contain numbers which are larger
> than can fit into long or ulong, it's an abnormal case. Many apps
> (probably, almost all) will want to reject such numbers immediately.
> BigInt should be opt-in.
> 
> And, it is also possible to have floating point numbers that are not
> representable in double or real. BigInt doesn't solve that case.
> 
> It might be adequate to simply present it as a raw number (an
> unconverted string) if it isn't a built-in type. Parse it for
> validity, but don't actually convert it.
[...]

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.)


T

-- 
Be in denial for long enough, and one day you'll deny yourself of things you wish you hadn't.