[boost] Re: mpl::begin<mpl::vector<...> > performance problem

From: David Abrahams (dave_at_[hidden])
Date: 2005-02-24 12:28:47

"Arkadiy Vertleyb" <vertleyb_at_[hidden]> writes:

> "David Abrahams" <dave_at_[hidden]> wrote in message
>
>> "Arkadiy Vertleyb" <vertleyb_at_[hidden]> writes:
>>
>> > Hi all,
>> >
>> > I am having a huge compile performance problem trying to use mpl::begin
> for
>> > an mpl::vector of a large size -- the complexity seems to be far from
>> > constant (or even linear) time.  The following example demonstrates it
> (I am
>> > using GCC 3.3.3 or 3.4.2)
>>
>> Are you sure you're not seeing preprocessor slowness?
>
> I modified the example to get the PP code out:
>
> typedef BOOST_PP_CAT(boost::mpl::vector, BOOST_TYPEOF_LIMIT_SIZE)<
> BOOST_PP_ENUM(BOOST_TYPEOF_LIMIT_SIZE, MACRO, ~)
>> v;
>
> #warning started getting begin
> typedef boost::mpl::begin<v>::type it;
> #warning done getting begin
>
> It takes about 35 seconds between two warnings....
>
> The similar problem seems to exist for at<>.  It takes forever to compile
> at<v, int_<0> > in the same context.

Well, we need to hear from Aleksey on this one, I guess.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com