[Opensim-dev] Change JSON constants to be able to act as independent flags?

[Justin Clark-Casey]

On 19/02/13 18:01, Mic Bowman wrote:
> I'm generally not in favor of bit fields. they are too hard to extend. two alternatives that might work based on the
> idea that there are really two pieces of information we want to convey... the type of the JSON node (null, object/hash,
> array, value) and the type of value in a value node.

An LSL integer would give you 31 bits to play with - do you envisage needing more than 31 constants (ignoring the 
potential to use negative constants)?  I'm also curious as to what extendability you're thinking of - JSON is unlikely 
to change.

>
> 0) take the OSD approach and just return the type of the node/value (which is where I had planned to end up), null is 0,
> hash/object is 1, array is 2, value is anything greater than 2, string is 3, integer 4, etc...

The caller then has to know that there is an order to the constants.  If I want to see if something is a value then I 
need to do > JSON_TYPE_VALUE whereas for any other type I would use ==, which doesn't feel particularly intuitive to me.

Using a flag approach also appears very common in LSL and would work more as scripters expect (using bit operators for 
comparison, etc.).  I know you're not a fan of LSL but I believe it's better to try and work with the grain where possible.

>
> 1) partition the return into a node type and value type. use the bottom three bits for node type and the rest for the
> value type if the node is a value node; this at least provides some space for future extensibility

I think a mixed bits and values approach is the worst of both worlds - callers then need to know which constants can be 
tested with bit operators and which cannot!

>
> 2) split the operations into two.. JsonGetNodeType() and JsonGetValueType()

You could do that.  It would match the JsonGetValue(), JsonSetValue(), etc. functions.  I would argue they are still 
both better off using flag constants for the reasons above.

>
> --mic
>
>
> On Mon, Feb 18, 2013 at 5:02 PM, Justin Clark-Casey <jjustincc at googlemail.com <mailto:jjustincc at googlemail.com>> wrote:
>
>     Hi Mic.  One small thing in case I don't catch you on IRC - could we change the Json node types to be independently
>     flaggable values rather than 0, 1, 2, 3 as they are at the moment?  That way, one would be able to more easily flag
>     a node as both Value and String in the future, for example.
>
>     --
>     Justin Clark-Casey (justincc)
>     OSVW Consulting
>     http://justincc.org
>     http://twitter.com/justincc
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-- 
Justin Clark-Casey (justincc)
OSVW Consulting
http://justincc.org
http://twitter.com/justincc