std.variant benchmark

[Andrei Alexandrescu]

On 7/29/12 10:43 AM, Dmitry Olshansky wrote:
> I'm horrified. Who was working on std.variant enhancements? Please chime
> in.

I guess you just volunteered! When I looked at it this morning I noticed 
a few signs of bit rot, e.g. opAssign returns by value and such. (Only 
planting a "ref" there improves performance a good amount.)

Variant has a simple design with (in case of int) an int and a pointer 
to a function. Many of its operations incur an indirect call through 
that pointer. This makes operations slower than the time-honored design 
of using an integral tag and switching on it, but offers in return the 
ability to hold any type without needing to enumerate all types explicitly.

We can use the pointer to function as a tag for improving performance on 
primitive types.


Andrei