fixed [over.match.list]-related problem with eager value_type

[joaquintides]

The following

#include <boost/container/hub.hpp>
#include <boost/any.hpp>

int main()
{
  boost::container::hub<boost::any> h;
}

fails in VS (and other compilers):

error C7535: 'boost::container::hub<boost::any,void>::hub': delegating constructor calls itself

This is due to a sequence of happenstances:

• boost::container::hub default ctor delegates to hub{allocator_type()} (note the braces).
• The braces, in connection with [over.match.list] and the fact that boost::any can be constructed from allocator_type (and from anything), make the compiler consider std::initializer_list construction.
• std::initializer_list construction delegates to hub{il.begin(), il.end(), al_}.
• hub{il.begin(), il.end(), al_} is again formally valid as constructing from a std::initializer_list of boost::anys, and recursion ensues.

The simple fix is replacing {...}-style construction with (...) everywhere (not only for the default constructor).

[igaztanaga]

Many thanks Joaquin!