Re: [Boost-users] [mpl] what is not a placeholder expression

on Fri Jul 27 2007, "JOAQUIN LOPEZ MU?Z" wrote:

According to the MPL reference, a placeholder expression X must satisfy (among others) the following condition:

"All of X's template parameters, including the default ones, are types."

According to that the following should then compile without errors:

#include #include #include

using namespace boost; using namespace boost::mpl;

template struct foo { template<typename Q> struct apply{ typedef Q type; }; };

typedef apply1,int>::type t1;

BOOST_MPL_ASSERT((is_same));

int main(){}

I don't see how you can conclude the above will compile without error just from (a part of) the definition of placeholder expression. Are you saying that since foo<_1> is not a placeholder expression, when applied to int it should be treated as a metafunction class? -- Dave Abrahams Boost Consulting http://www.boost-consulting.com The Astoria Seminar ==> http://www.astoriaseminar.com