Fernando Cacciola wrote:
Pendantically speaking, there is no such thing as a "safe reinterpret_cast". While this is somewhat permmited in production code where the typical deadline is yesterday, here in boost you need a definite need for using
that. Anyway, can you explain in some detail how doesn't your adaptation pattern avoid copying?
The ability to modify the contents of an object in place without copying was the original intent of the entire exercise in generic programming. If you have two classes class A {...}; class B : public A {...}; or by composition class A {...}; class B { A a; }; You know it is safe to reinterpret_cast A to B and B to A (because they are the same data, and differ in behavior only.) You can take an object of type A, cast it to B, use the behaviors of B to modify it *in place* and cast it back to an A if you like. I don't believe that reinterpret_cast shouldn't be permitted. There are cases where reading the C++ standard will inform a developer that reinterpret_cast is safe and if the compiler causes a problem it is because of a problem in the compiler, not the code. Specifically, I submit that inheritance and composition are such cases provided that additional data members are not added in the subtype or composed type. I don't make the user reinterpret_cast for themselves, but instead provide mimic() and yield() functions for casting to and from my Concept type. If this use of reinterpret_cast to change the behavior of an object is unacceptable for a boost submission that pretty much closes the whole case, since the design pattern depends upon it in a very necessary way. Obviously, we should sort this issue out. There was once an experiment on group learning conducted on monkeys. A group of monkeys in a cage had an electrified banana lowered into it periodically. They quickly learned not to touch it. When new monkeys were introduced into the cage the other monkeys went to extreme measures to prevent them from touching the electric banana. Old monkeys were removed and new monkeys added until eventually no monkey present had ever touched or seen another monkey touch the banana, but still they prevented any new monkey from breaking the taboo. At that point it became impossible for the monkeys to ever learn that the banana was safe, because even if they touched it and didn't get shocked they wouldn't know that the circumstance had changed. Luke