[LC++]How to use const member functions correctly?

Davide Bolcioni 9odb6x3rfr001 at sneakemail.com
Sun Sep 23 06:58:04 UTC 2001

Carlo Wood carlo at alinoe.com [mltuxcpp/linux-cpp list] wrote:

>>   c1.f(c1); // Sets c1.n to 3 ... oops, const changed.
> No oops imho, 'c1' changed - which is ok because 'c1' was NOT constant.
> If you'd try:
> C const c1;
> ...
> c1.f(c1);
> then the compiler would complain.  So the code is perfectly safe.

Yes, I agree; the point of "oops" is that the "const" member
function .f() changed c1, the instance is it applied to - so
you find c1 changed in a place where you would not expect to
in real code, where the aliasing would not be so obvious.

Your suggestion

   assert(&arg != this);

seems entirely appropriate for const member functions taking a
modifiable reference or pointer argument to their type (or an
ancestor, I guess) just to guard against this surprise.

With multiple inheritance or when operator& is redefined things
may need more care, but the reasoning I agree with entirely.

Davide Bolcioni
There is no place like /home.

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