* Ethan Furman:
Steve Howell wrote:
Going back to pointers vs. references, I think the key distinction
being made is that pointers allow specific memory manipulation,
although I think even there you're really just dealing with
abstractions. The address 0x78F394D2 is a little bit closer to the
machine than, say, the 42nd element of a Python list, but they are
both just abstractions on top of underlying machines, whether the
machines are virtual, electronic circuits, vacuum tubes, whatever.
You can add 6 to 42 and get the 48th object, but its Python's
convention not to call the 48th object a memory address or expose a
reference to it as a pointer. If I want to pass along the reference
to the 48th element of a list as the slot to be updated (i.e. with the
intention to actually mutate the list itself), then I need a tuple
like (lst, 48).
I think that's the key right there -- if 48 was really a pointer, you
wouldn't need to pass lst in as 48 would in fact be the memory address
of the object you wanted to manipulate.
The generalization is known as a "based pointer".
Except where it's a fundamental abstraction in a programming language, where it
might be called anything.
For example, in C++ some so called "member pointers" are logically based
pointers. They have pointer syntax (as do C++ iterators, which are not
necessarily pointers), but member pointers are not pointers in the C++
standard's sense; in particular, dereferencing a C++ member pointer yields a
typeless entity, which is not the case for a normal pointer, although that
standard confusingly calls also member pointers pointers in some places, and in
other places uses the pointer term only about basic pointers.
So, delving into the details of that terminology means traveling into a pretty
chaotic territory. But on the other hand, going for the more abstract it gets
cleaner and simpler. The Wikipedia article is about in the middle somewhere.
It is perhaps not confusing that it is confusing to many. :-)
Cheers & hth.,
- Alf
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