problem implementing getter/setter

[aj3423]

Hi,

I'm implementing a property class for gui library, just like property in vb
for example

struct window {
  property::rw<string> title;
  ...
};
window w(...);
w.create(); // displays a new win32 window
w.title = "new title"; // then the window title is changed 

this is the implementation, seems not working
http://liveworkspace.org/code/3zLDWs$4

#include <functional>
#include <iostream>
using namespace std;

namespace property {

   template<typename T>
	struct value_holder {
		T val;
		value_holder() : val(T()) {}
	};

	template<typename T, typename RW>
	struct read {
		function<T()> getter;
		operator T() {
			if(getter) return getter();
			return ((RW*)this)->val; // how to access value_holder::val
		}
	};

	template<typename T, typename RW>
	struct write {
		function<void(const T&)> setter;
		void operator=(const T& new_val) {
			((RW*)this)->val = new_val;
			if(setter) setter(new_val);
		}
	};

	// -------- r / w / rw -----------
	template<typename T>
	struct r
		: value_holder<T>
		, read<T, r<T>>
	{
	};
	template<typename T>
	struct w
		: public value_holder<T>
		, public write<T, w<T>>
	{
		using write<T, w<T>>::operator=;
	};
	template<typename T>
	struct rw
		: value_holder<T>
		, read<T, r<T>>
		, write<T, w<T>>
	{
		using write<T, w<T>>::operator=;
	};

}


int main() {

   property::rw<int> p;

	p = 3; //write access

	int x = p; //read access

	cout << x << endl;// why output 0

}

[Disch]

It was crashing for me when I tried to run it. The problem is you're doing a bad cast.

Specifically, your rw struct is specifying the wrong RW template parameter:

	template<typename T>
	struct rw
		: value_holder<T>
		, read<T, /*r<T>*/ rw<T> >
		, write<T, /*w<T>*/ rw<T> >
	{
		using write<T, /*w<T>*/ rw<T>>::operator=;
	};

With those changes it works for me.

[aj3423]

Tanks a lot, what a stupid mistake.