Peter Dimov wrote:

It doesn't matter. Properties represent degrees of freedom. They don't describe dependent data well.

As a relatively simple example, consider a pair of integers (x, y) that has an invariant of x*x + y*y = 25, and try to move from (3, 4) to (4, 3) by using the X and Y properties.

Since the invariant is on both variables, neither can be set independant of each other, since you'd assume that changing one would invalidate the invariant. Therefore, the properties must be *readonly* to prevent modification. You'd have a function to set both values at the same time (e.g. moveto). class coord { private: int x, y; public: inline int get_X(){ return( x ); } inline int get_Y(){ return( y ); } inline void moveto( int x_, int y_ ) { assery(( x_ * x_ ) + ( y_ * y_ ) == 25 ); // invariant x = x_; y = y_; } public: // data access property_readonly< int, &get_X > X; property_readonly< int, &get_Y > Y; public: // ... }; Regards, Reece _________________________________________________________________ It's fast, it's easy and it's free. Get MSN Messenger today! http://www.msn.co.uk/messenger