Re: [Boost-users] Why use 'functional composition' with boost::bind

Subject: Re: [Boost-users] Why use 'functional composition' with boost::bind
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2010-08-04 23:29:54

On Wed, Aug 4, 2010 at 2:06 PM, David Abrahams <dave_at_[hidden]> wrote:
>
> On Aug 4, 2010, at 3:22 PM, WB wrote:
>
>> Case 3 runs in ~1.8...1.9s, case 1 and 2 in 0.81...0.84s.
>> This is the same ratio I already had (at least I'm not
>> confused about that). So your 0.65s for case 3 is
>> really amazing.
>
> Knowing nothing about your particular code... chances are good that somebody is not measuring what he thinks he's measuring. Â If you want a sample of the kinds of issues you should consider, have a look at http://github.com/boost-lib/parameter/blob/master/test/efficiency.cpp

Again, try this in phoenix:
  boost::transform(v, arg1 * 2);

The arg1 * 2 creates this same thing:
struct anonymousThing
{
  template<typename T>
  T operator(const T& t) const
  {
    return t * 2;
  }
}

So the above executes something like this:
  boost:;transform(v, anonymousThing());

Which the compiler should rather well optimize completely out, at
least it always does for me in VC.

You can also use _1 in phoenix (*IF* you pull it from the phoenix
namespace and you do *NOT* include boost/bind.hpp), but arg1 is better
as it is completely unambiguous so you have no worry.