Hi Yasuo, > > Now I understand what you are discussing. Since we may have stricter > typing, we probably better > to consider type safety theory even if PHP is weakly typed.
I am not sure it was about types, it was about conditions... > Pre/Postconditions should be checked only when parent method is called. > That's what Eiffel does. > Eiffel does not allow method overriding. Therefore, pre/postconditions of > methods (not invariants. > Invariants inherited implicitly(automatically) both Eiffel and D are > evaluated except certain > methods) cannot be evaluated automatically unless parent method is called. I agree for pre-conditions, but not sure for post-conditions. > Since children's method may have whole different way of handing > parameters, > including swapping parameter order, adding/removing parameters, etc. > Parameters cannot be checked automatically unless we have some kind of > binding system that bind child parameter to parent parameter. Even if we > have > it, parameter for parents may be generated in function body. It cannot be > perfect. I hadn't thought about this. Parent and derived methods can have different signatures. So, you mean we cannot inherit pre/post-conditions in any way. But what about interfaces, as the signature matches there ? The interface case is complex, as a class can implement more than one interface and interfaces can be extended, providing the same potential problems as multiple inheritance. The parent's post-conditions should be checked too, but in the parent scope, which is probably impossible (using parent argument names). To solve this, we can split post-conditions to two sets : those which deal with the return type and value only, and those that check other conditions (passed by ref args, for instance). Then, the parent's post-conditions which deal with return value only can be checked when the derived methods exit. > Basic rule is we shouldn't be able to modify parent contracts(invariant, > methods pre/postconditions). > If we can change it, it's the same as changing type. Your discussion > applies to invariant and this > is what you write, I suppose. I am not sure I understand what you mean with 'modify parent contract'. If you mean that we must apply total inheritance for invariants, I agree. > The same rule for class applies to interfaces. ?? I don't understand. > We cannot ignore parent class invariants. If developer violate parent > property restrictions, > it's violation of parent class type and this must be forbidden. It's > checked by invariant contract. I agree. Regards François -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
