Re: [boost] determine first arg of callable

15 May 2013

      13/5/15 Andrey Semashev 
...
On Wed, May 15, 2013 at 5:38 PM, Oliver Kowalke 
...
wrote:
...
the class has to accept a callable object (function pointer or functor) -
what is known is that it does return void and takes one argument.
this is not a design decision, it is required by the user.
as I showed in my example it can be solved - maybe a solution would be to
overload the ctor with the type returned by boost::bind().
The bind function objects do not have a single operator(), and their
operators() are templates.
OK - some simple code:

struct B
{
  virtual void run() = 0;
};

template< typename Fn >
struct D : public B
{
  Fn fn;

  D( Fn fn_) : fn( fn_) {}

  void run() { fn(...) } // argument construction omitted
};

struct X
{
  B * b;

  template< typename Fn >
  X( Fn fn) : b( 0)
  {
     b = new D< Fn >( fn);
  }

  void run() { b->run(); }
};

Constraints to Fn: returns void and has only one argument.
I need to know in X::X() or D::run() what's the first and only argument of
Fn.
I believe the problem should be solvable - for function pointers it is
easy, X() could be overloaded with function<>.
The only remaining issue are objects created by bind() and passed to the
ctor - I thought overloading X() with the type returned by bind() should
work?!