Tobias Schwinger <tschwinger@neoscientists.org> writes:

Hi,

This code:

#include <boost/mpl/vector.hpp> #include <boost/mpl/pop_front.hpp> #include <boost/mpl/assert.hpp> #include <boost/mpl/equal.hpp>

using namespace boost;

// Doc says: pop_front returns a vector typedef mpl::pop_front< mpl::vector<bool,char,int> >::type v;

// Doc says: vectors have a type member equal to itself BOOST_MPL_ASSERT(( mpl::equal< v, v::type > ));

fails to compile with GCC ( v::type is mpl::vector3<bool,char,int> )

That's a bug. If that's truly happening, the documentation is correct and the implementation is wrong.

and compiles fine with other compilers.

Examples for false conclusions that could be easily drawn from the current documentation:

"Oh great - I do not need mpl::identity when using v with mpl::eval_if"

"Let's inherit from 'v::type' so I can save the '::type' later"

"::type always gives the numbered form of my current sequence so I can use it with partial specialization"

I got trapped by this in two different places (and I still hope not to be surpassingly stupid ;-). Shouldn't this behaviour be documented in some way ?

No, it should be fixed. mpl::pop_front< mpl::vector<bool,char,int> >::type::type should always be a sequence of length 2 containing (char, int). -- Dave Abrahams Boost Consulting www.boost-consulting.com