Re: [boost] Request for interest in a library to ease double dispatching

Subject: Re: [boost] Request for interest in a library to ease double dispatching
From: Larry Evans (cppljevans_at_[hidden])
Date: 2012-12-03 12:55:07

On 12/03/12 11:40, Larry Evans wrote:
> On 12/03/12 08:13, Per Karlström wrote:
[snip]
>> I have been tinkering on a template library to ease the use of double
>> dispatching. Now I know there are other techniques such as visitor
>> patterns that might solve this problem in a more general way. However I
>> believe that there are occasions when using double dispatch is a good
>> way forward. I have some excerpts of example code at the end of this mail.
>>
>> Of course if I somehow have missed a boost library that already handles
>> this I would be happy to know about it.
[snip]
>
> There's multiple dispatch code here:
> 
> 
> http://svn.boost.org/svn/boost/sandbox/variadic_templates/libs/composite_storage/sandbox/pack/
> 
> The predator_prey.cpp uses virtual functions for dispatching.
> The one_of_multiple_dispatch.test.cpp
> uses either virtual functions or switches to do the dispatching.
> 
> Unfortunately, I found the timing was pretty slow on the
> one_of_multiple_dispatch vs. the variant visitor :(

I meant the compile times were slow.  I didn't bother with
runtimes.  Also, I provided a switch implementation because
others (in this NG, IIRC) have said that was faster than
virtual functions for dispatching.

Anyway, the timing results are attached for a clang compiler.
The table shows the ratio of the times w.r.t. an implementation
called CLOPTR, which was posted in the earlier post on boost.user:

From: Paul <peebor_at_[hidden]>
Newsgroups: gmane.comp.lib.boost.user
Subject: Re: large variant performance compared (50 elements)
Date: Thu, 27 Jan 2011 20:19:08 +0100

-regards,
Larry