Re: [boost] [proto] design of expr<>

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-10 14:45:17

On 03/10/08 11:29, Eric Niebler wrote:
> Steven Watanabe wrote:
>> AMDG
>>
>> Markus Werle wrote:
[snip]
> 
> The typelist used there is not Fusion-compatible, but expr<> as a whole 
> is. For a while, I was using mpl::vector<> as the second template 
> parameter to expr<>, but I changed to a very simple custom type because 
> it improved compile times.
> 

Could you give some estimate as to how much it improved
compile times?  Do you have handy a benchmark test to show
this?  I would like to try this benchmark with the variadic
template compiler to see how close they are.

I know you've already tried the variadic compiler, but I'd
like to try the benchmark myself and maybe show the results
and code to Douglas Gregor so that maybe he can figure out
why the variadic compiler is not improving compile times.
As you noted in a private email to me, the basic
reason is:

   Instantiating templates is expensive. By comparison,
   expanding a macro is cheap.

However, maybe the benchmark would prompt Douglas to look
for ways to improve the compiler's template instantiation
speed.