template<class T>
struct Property
{
	typedef Callback1<const T&> S;
	typedef Callback1<T&> G;

	Property(const S& s, const G& g)
		: set(s), get(g) {}

	const T& Set(const T& a) { ASSERT(set); set(a); return a; }
	T Get() const { ASSERT(get); T t; get(t); return t; }

	inline T operator= (const T& a) { return Set(a); }
	inline operator T() const { return Get(); }

public:
	const S set;
	const G get;
};

typedef Property<Value> PropertyValue;

...

//.h
class PropertyTest : public WithPropertyTestLayout<TopWindow> {
public:
	typedef PropertyTest CLASSNAME;
	PropertyTest();
	
	void GetD(Value& a) { a = "abc"; }
	void SetD(const Value& a) { RLOG(a); }
	
	PropertyValue vp;
};

//.cpp
PropertyTest::PropertyTest()

#pragma warning(push)
#pragma warning(disable:4355)
	: vp( THISBACK(SetD), THISBACK(GetD) )
#pragma warning(pop)

{
	CtrlLayout(*this, "Window title");

	//setting, will call SetD
	vp = 123;

	//getting, will call GetD
	Value v = vp;
	RLOG(v);
}

GUI_APP_MAIN
{
	PropertyTest().Run();
}

EditInt ei;

ei.min = 100;
ei.max = 200;
ei.data = 150;
ei.show = true;
ei.rect = Rect(0,0, 100,200);
...