[fpc-pascal] JSON register new data types for custom output/input

[Graeme Geldenhuys]

On 2016-05-17 12:23, Michael Van Canneyt wrote:
> There cannot be custom output in JSON, then it would no longer be JSON. 
> JSON is a fixed defined format; it does not allow "deviation".

Maybe you understood me wrong, or my output examples were rubbish - you
pick. ;-) I don't mean generating non-standard JSON output. The output
will still be true JSON, just in a improved format for multiple
applications (not just FPC or Delphi based) to understand.

eg:
Here is a snippet of a JavaScript based Report Designer that outputs
colour values to JSON:

      "Brush": "solid:77,182,172",
      "TextBrush": "solid:255,255,255",

Note, it is still valid JSON, but it is an improved output format that
most likely multiple application could understand better than the
original TColor value.

Now obviously I can manually format TColor to the above string output,
and than parse the string data when read again. I would have to do this
at all places where I save/read a TColor value.

My suggestion is if one could register a TColor reader/writer type, and
fpjson can then do the rest - using the helper classes when needed. I
would only have to register this new type once in my application, and
persisting TColor could be simpler in my code.

Granted, I haven't given this much thought - it's just an idea that
popped up. So there is most likely some details or usage idea that need
to be worked out.


Another useful example would be persisting enum types. Currently I have
to write functions like StretchTypeToString() and StringToStretchType()
and then use these all over my code where I read/write a TStretchType
value. I'm hoping the above idea could simplify code like this too.

Regards,
  Graeme

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