Why can't I visit this custom type with boost::variant?

Question

The following code:

#include 
#include 
#include 

struct A
{
    A()
    {
    }
    ~A() throw()
            


        

Answer 1

message_t a(A());

Has the most-vexing-parse problem: declares a function rather than creates a variable. Many ways to resolve, e.g. message_t a = A();