Re: [boost] patch - performance problem in boost string algorithms

From: Shunsuke Sogame (mb2act_at_[hidden])
Date: 2006-07-21 02:26:04

Pavol Droba wrote:
> Hi,
> 
> First of all, I'd like to thank you for the nice benchmarks.
> 
> Now my comments to your patches:
> 
> 1.) const Predicate& Pred
> Although this change can bring a performance benefits, it has one big
> drawback. You cannot pass an ordinary C function as predicate.
> At least not in VC++ 7.1
> 
> Following code will not work:
> 
> int func(int a)
> {
> 	return a+2;
> }
> 
> template<typename TFunc>
> int sum(TFunc f, unsigned int a)
> {
> 	int acum=0;
> 	for(unsigned int i=0; i<a; i++)
> 	{
> 		acum+=f(i);
> 	}
> 	
> 	return acum;
> }
> 
> ...
> 
> sum(func, 1000);

It is surprising for me.
VC++ seems to need overloads:

     int func(int a)
     {
         return a+2;
     }

     struct func_t
     {
         int operator()(int a) const
         {
             return a+2;
         }
     };

     template<typename TFunc>
     int sum_aux(TFunc& f, unsigned int a)
     {
         int acum=0;
         for(unsigned int i=0; i<a; i++)
         {
             acum+=f(i);
         }

         return acum;
     }

     template<typename TFunc>
     int sum(TFunc const& f, unsigned int a)
     {
         return ::sum_aux(f, a);
     }

     template<typename TFunc>
     int sum(TFunc& f, unsigned int a)
     {
         return ::sum_aux(f, a);
     }

     void test()
     {
         ::sum(::func, 1000);
         ::sum(&::func, 1000);
         ::sum(::func_t(), 1000);
     }

Looks working well under gcc and vc.
But, the forwarding problem will come...

-- 
Shunsuke Sogame