Re: [boost] If boost::fusion is the hammer, then what's the nail?

From: Joel de Guzman (joel_at_[hidden])
Date: 2006-12-15 16:49:14

Gennadiy Rozental wrote:
> "Joel de Guzman" <joel_at_[hidden]> wrote in message 
> news:elskhd$b32$2_at_sea.gmane.org...
>> Gennadiy Rozental wrote:
>>> "John Maddock" <john_at_[hidden]> wrote in message
>>> news:006401c71f85$12d1a8b0$20570252_at_fuji...
>>>> Weapon Liu wrote:
>>>>> I personally very like this fancy facility, and that's why I present
>>>>> these mumbles here to annoy you guys( if so, my apologies go here:-))
>>>>> Any comments?
>>>> I can give you one use I have for tuples:
>>>>
>>>> I have a piece of boilerplate code that accepts a tuple (of any size) 
>>>> and
>>>> prints out either a csv file or a boost::array C++ code conaining the 
>>>> data
>>>> passed.
>>>>
>>>> It allows me to output data for graphing, or matrixes of test data very
>>>> quickly just by creating a short function that returns a tuple, and then
>>>> passing that function to my boilerplate.  If I want more columns of data 
>>>> I
>>>> just increase the size of tuple by 1.
>>>>
>>>> I suppose I could have used a vector instead, but it's less elegant
>>>> somehow.
>>> How the std::vector<boost::variant> is less elegant?
>>>
>>> 1. It's could be implemented in cpp file. Your tuple based solution is in
>>> header right?
>>> 2. It allows dynamically sized entries, so you could skip some of the
>>> default values
>>> 3. It's as fast of could be even faster since we don't need to pass big
>>> structures around
>>>
>>> The only drawback is that you need to know set of types ahead of time. 
>>> But
>>> this is minor IMO and it's quite easy to add an extra type whether a need
>>> arise.
>> Another drawback of std::vector<boost::variant> is speed, of course.
> 
> This is not clear cut. I do not see in theory why any boost::variant based 
> algorithm couldn't be optimized to almost the same code (module type 
> switching). On the other hand excessive usage of tuples will cause 
> appropriate code bloat, eventually leading to code slow down.

Test it; profile it. You'll see what I mean :)

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net