In the simple case of using memory location as object identity (ie. in system without moving GC) and typical textbook hashtable implementation simply using the

In the simple case of using memory location as object identity (ie. in system without moving GC) and typical textbook hashtable implementation simply using the pointer as hash value is highly suboptimal, because heap pointers do not have remotely uniform distribution (low order bits are always zero due to allignment constraints, high order bits tend to be constant and usually also zero...). On the other hand you can use more advanced hashtable design that is explicitly tuned for non-uniform hash value distribution. See CPythons dict for cannonical example of that, although it's motivations are somewhat different (the major reason is that in CPython even real hash values of object's content are intentionally non-uniform to allow for simple way of causing integer-valued floats to have same hash value as ints of same value).