[Boost-users] bind (excessive?) argument copying

From: Trent Hill (trent.hill_at_[hidden])
Date: 2005-01-04 22:11:19

I was recently surprised to find that boost::bind seems to copy 
arguments a number of times when called. For example, this program:

     class C
     {
     public:
         C() {}
         C(const C &c) : data(c.data) { std::cout << "C(const C &c)\n"; }
         boost::array<char, 4000> data;
     };

     void foo(const C &) {}

     int
     main(int a_argc, char **a_argv)
     {
         C c;
         boost::bind(&foo, c);
         return EXIT_SUCCESS;
     }

results in this output (Visual C++ .NET with /O2):

     C(const C &c)
     C(const C &c)
     C(const C &c)
     C(const C &c)

Four copies - I had hoped to only see a single copy. Logically, there 
doesn't seem to be a need for more than one copy. Is there an 
implementation issue that requires this many copies?

I was hoping to use bind with some moderately weighted objects, however 
the number of copies that seem to occur may be prohibitive for me. (I 
realise that dynamically allocating objects and passing around pointers 
is an alternative but I'd rather avoid that if possible.)

Any thoughts?
Thanks, Trent.