std.data.json formal review

[Dmitry Olshansky via Digitalmars-d]

On 18-Aug-2015 16:19, Andrei Alexandrescu wrote:
> On 8/18/15 2:55 AM, Dmitry Olshansky wrote:
>> On 18-Aug-2015 01:33, Andrei Alexandrescu wrote:
>>> On 8/17/15 2:47 PM, Dmitry Olshansky wrote:
>>>>
>>>> Actually one can combine the two:
>>>> - use integer type tag for everything built-in
>>>> - use pointer tag for what is not
>>>
>>> But a pointer tag can do everything that an integer tag does. -- Andrei
>>
>> albeit quite a deal slooower.
>
> I think there's a misunderstanding. Pointers _are_ 64-bit integers and
> may be compared as such. You can use a pointer as an integer. -- Andrei
>

Integer in a small range is faster to switch on. Plus comparing to zero 
is faster, so if the common type has tag == 0 it's a net gain.

Strictly speaking pointer with vtbl is about as fast as switch but when 
we have to switch on 2 types the vtbl dispatch needs to be based on 2 
types instead of one. So ideally we need vtbl per pair of type to 
support e.g. fast binary operators on TaggedAlgebraic.

-- 
Dmitry Olshansky