From: David Abrahams (dave_at_[hidden])
Date: 2005-03-03 17:49:35
Tobias Schwinger <tschwinger_at_[hidden]> writes:
> 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
> 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
> "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
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