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From: Reece Dunn (msclrhd_at_[hidden])
Date: 20040524 08:51:56
Peter Dimov wrote:
>Reece Dunn wrote:
> > Peter Dimov wrote:
> >> 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.
It all depends on what you are using the properties for. I use them
regularly when dealing with MS COM objects where the interfaces use get/set
methods to interface with the underlying object. So you can use them more
intuitively (especially when coupled with smart pointers, exceptions and
variant/BSTR helpers):
com::msxml::XMLDOMNode node = ...;
std::cout << node.nodeName << " = " << node.nodeValue << '\n';
which would look very ugly without properties!
Regards,
Reece
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