std.variant benchmark

[jerro]

>> I profiled it and found out much of the time is spent inside
>> TypeInfo.opEquals being called from tryPutting. So I tried 
>> replacing "!=
>> typeid" in tryPutting with "!is typeid". That brought the time 
>> from 2.8 s
>> down to 0.12 on my machine. I don't know if that is the proper 
>> solution,
>> since I don't know if typeid can ever return two TypeInfo 
>> objects that
>> aren't the same but are equal (I haven't used typeid and 
>> TypeInfo much
>> before). The fib function here does return correct result 
>> after doing that,
>> though.
>>
>
> Wow! Now that's an impressive improvement. If TypeInfo 
> instances are unique
> for every type, then we should be good to go!

I've tried Dmitry's fork now (he optimized opArithmetic to not do 
as many calls to fptr) and it's even a little faster (1.01 s for 
100000 iterations). Replacing != with !is in Dmitry's fork speeds 
it up a little bit more (0.935 s for 100000 iterations).