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From: Daniel James (daniel_at_[hidden])
Date: 2005-10-09 04:58:21

Alexander Nasonov wrote:
> That's not quite right. For example
> #include <iostream>
> #include <boost/functional/hash.hpp>
> struct Base
> {
> bool operator==(Base) const { return true; }
> };
> std::size_t hash_value(Base)
> {
> return 0; // Base has no state
> }
> struct Derived : Base
> {
> int dummy;
> bool operator==(Derived other) const { return dummy == other.dummy; }
> };

OK, I thought you meant something else. It seems to me that in this
case, hash_value(Base) is a part of Base's interface - so any class that
derives from it should take it into account. It also appears that Base
wasn't really designed for derivation (despite its name ;), and it's
generally a bad idea to derive from such classes. I guess that's a bit
of a cop out answer, but this is more of a problem with the way the
derivation is done than Boost.Hash itself.

What I should do, is add some documentation about using Boost.Hash with
class inheritance. I'll try to do that soon-ish.

What do you think about having a macro to disable the extensions? Am I
right in thinking that your main concern is that the extensions are in

Sorry for the late reply,


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