Re: [Boost-users] MPL intersection of type sequences and compile-time performance

11 Jun 2007

      Hi,

Than you for the quick reply :) Now I reimplemented
intersect by converting the type sequences to mpl::set
and do a mpl::has_key instead of mpl::contains:

template 
struct intersect
{
  typedef typename copy, insert< _1, _2 > >
     >::type set_seq2;

  typedef typename copy_if 
     , back_inserter < vector<> >
     >::type type;
};

Now I would like to optimize this and only convert to
a set if the type sequence does not support
mpl::has_key. How should I do this?

I looked at the mpl::sequence_tag<seq2> but I am not
sure how to use this. Nor if this is the right way to
do this. Could you please help?

Thanks,
Andrej

--- David Abrahams  wrote:
...
on Sun Jun 10 2007, Andrej van der Zee
 wrote:
...
Hi,
Sorry if this already has been posted, but I have
a
problem with compile-time performance when trying
to
get the intersection of two type sequences. For
example, when I do something like this:
template
struct intersect
{
  typedef typename boost::mpl::remove_if
...
::type type;
};
typedef mpl::vector l1;
typedef mpl::vector l2;
typename intersect::type
my_intersection;
Then for large type sequences compile-time becomes
unacceptable (O(M*N)).
I'm surprised it's even that good, since most
compilers have such poor
performance for multiple instantiations of the same
template.  That's
the cost you'd expect for a direct runtime
translation of your
algorithm.
...
Is there a better way to do this?
I'd use an associative sequence like mpl::set.
-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com
_______________________________________________
Boost-users mailing list
Boost-users@lists.boost.org
http://lists.boost.org/mailman/listinfo.cgi/boost-users
...
___________________________________________________________ 
Yahoo! Mail is the world's favourite email. Don't settle for less, sign up for
your free account today http://uk.rd.yahoo.com/evt=44106/*http://uk.docs.yahoo.com/mail/winter07.htm...