2013/5/16 Oliver Kowalke
2013/5/15 Peter Dimov
This still doesn't quite explain it. Let's say that my fn takes a std::string. How does D know what string to pass? An empty string? "foo"? "hello world"? Where does the argument value come from?
Fn does takes a Q< std::string > not a plain std::string (I've omitted this detail in my first example). Q<> might be default constructable.
template< typename Arg > struct Q {...};
does something irrelevant
struct B { virtual void run() = 0; };
interface
template< typename Fn, typename Arg > struct D : public B { Fn fn;
D( Fn fn_) : fn( fn_) {}
void run() { Q< Arg > q; fn( q) } // argument construction omitted };
concrete implementation - calls default ctor of Q< Arg > in D::run() and passes instance of Q< Arg > to fn
struct X { B * b;
template< typename Fn > X( Fn fn) : b( 0) { typedef typename Magic< Fn >::arg1_type arg_type; b = new D< Fn, arg_type >( fn); }
void run() { b->run(); } };
bundles the stuff
void g( Q< std::string > &) {...} X x( g); x.run(); // call g() with an instance of Q< std::string > as arg
struct W { void h( Q< int > &) {...} }; W w; X x( bind( & W::h, w, _1) ); x.run(); // call W::h() with an instance of Q< int > as arg
I can hardly imagine the real use case.
Will the following acceptable?
X x(feed