Reece Dunn wrote:
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).
Exactly. Which is the C++ model: int x() const, int y() const, void set(int, int). Some purists even omit the set(): p = point(4, 3); You can, of course, use "read only properties" instead of x() and y() but this changes nothing but syntax, not necessarily for the better, I might add.