id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
5637,use of mpl::print imposes default constructible requirement on argument,Robert Ramey,Aleksey Gurtovoy,"I'm using the following to debug some TMP code that looks like the following.
{{{
#include <boost/mpl/print.hpp>
struct X {
    X(int);
};

boost::mpl::print< 
    X 
>::type x;

boost::mpl::print< 
    X 
>::type y;
}}}

I get an error message that the type X is not default constructible.  A little investigation yields the definition of mpl::print (simplified for exposition)

{{{
template <class T>
struct print : identity<T>
{
    enum { n = sizeof(T) + -1 };
};
}}}

So invoking the print creates an instance with the default constructor
which provokes the error in this case.  For my purposes, I made the following change which seems to address the problem:

{{{
template <class T>
struct print : identity<T *>
{
    enum { n = sizeof(T) + -1 };
};
}}}

I'm using MSVC 9.0.

A couple of misceleanous issues besides this:

On my current version of GCC - 4.3.4 I get no warning at all.

If the same type is printed more than once, I only get the warning on the first instance.  

Robert Ramey

",Tasks,new,To Be Determined,mpl,Boost 1.46.1,Problem,,mpl print,