Re: [Boost-users] [mpl] newbie question

From: Andy Little (andy_at_[hidden])
Date: 2006-03-01 11:51:06

James Jones wrote
> Andy Little wrote:
>> Of course If anyone can implement the dimensional-analysis part of pqs
>> (in the Boost vault in The Physical Quantities Units directory) , such
>> that it compiles faster than it does currently, by using mpl, then I
>> will  be happy to re-implement it using mpl.
>
> If I recall previous posts correctly, the compile-time using MPL was 30
> seconds, and using your own code 4 seconds. Is this really a good reason not
> to use MPL? I would understand if it were 30 *minutes* versus 4 seconds. But
> in this case you're gaining 26 seconds per compile at the price of writing
> some custom code that may or may not be as maintainable as MPL (not saying it
> isn't - I haven't looked at pqs).
>
> I think in general it's understood that C++ in general, and BOOST in
> particular, can tend to increase compile times, because they heavily invest in
> compile-time template logic. But as I see it, an extra 26 seconds per compile
> times, say, 1000 compilations (to be generous) on a given project, is about
> one man-day (really less: it's 7-1/4 hours; how many of us put in only that
> much in a given workday?). Do you think it takes less than a man-day to come
> up with an MPL replacement, even one that only handles a subset of the
> functionality? Maybe, but I think there's reason to be skeptical.
>
> Also, if MPL resulted in a 7-times slower *runtime* than custom code, then
> choosing not to use might make more sense. Is that the case? If so, I missed
> it.
>
> Anyway, not saying you made the wrong decision, just offering a possible
> alternative way to think about this.

I think its best if I just leave my reply as "No comment ".  ;-)

regards
Andy Little