Pointers to functions

Question

I have to pass function into pointer. For this purposes I'm using boost::function. The function which catches the pointer is overloaded for different signatures. For example:

void Foo(boost::function<int ()>) { ... }
void Foo(boost::function<float ()>) { ... }
void Foo(boost::function<double ()>) { ... }

Now I wanna pass some class-method pointer there:

class test
{
   public:
      float toCall() { };
};

class Wrapper
{
  Wrapper() {
    test obj;
    Foo(boost::bind(&test::toCall, this));
  }
};


error: no matching function for call to ‘Foo(boost::_bi::bind_t<float, boost::_mfi::mf0<float, test>, boost::_bi::list1<boost::_bi::value<Wrapper*> > >)’
    note: candidates are: Foo(boost::function<float()>&)

Answer 1

Nonono this cannot work. Because boost::function<...> has a templated constructor to accept any and all types. Compatibility with the call signature is checked later on. Overload resolution cannot resolve this.

Also, i think you want to pass &obj instead of this. Try converting explicitly:

Foo(boost::function<float ()>(boost::bind(&test::toCall, &obj)));

This is utterly ugly though so you may want to introduce a typedef

void Foo(FloatHandler) { ... }
...
FloatHandler f(boost::bind(&test::toCall, &obj));
Foo(f);

Or ultimately you could make Foo a template that accepts just any callable type T. I suspect that may be the simplest, because in the general case i suspect you don't know to what boost::function<...> you need to cast to. And how about folks that want to return a std::complex<>. So...

template<typename T>
void Foo(T) { ... }
...
Foo(boost::bind(&test::toCall, &obj));

Hope this helps.