In-Reply-To: <019d01c52985$a04f54f0$6801a8c0@pdimov> pdimov@mmltd.net (Peter Dimov) wrote (abridged):
You also need equal_ptr<MyType>.
Indeed.
Also, it is easy to break the above unordered_set my modifying some of the MyTypes.
Yes, that's something to be aware of. I use the approach on types which are immutable, so it doesn't arise.
size_t Derived::hash_value() const { size_t seed = my_unique_value;
hash_combine( seed, Base::hash_value() ); hash_combine( seed, m_value );
return seed; }
That leaves the problem of assigning a different my_unique_value to each subclass, bearing in mind that different subclasses may be written by different people, teams or organisations. Without some kind of system people may just copy and paste code from one class to another and not change the value. -- Dave Harris, Nottingham, UK