On Sat, 12 Sep 2015 02:42 pm, Random832 wrote: > Anyway, maybe we do need a term to distinguish Python/C#/Java pointers > from C/C++ pointers - maybe call it a "non-arithmetic" pointer, since > the key thing about it is you can't do pointer arithmetic on them to get > the object "next to" the one it points at.
How about *just don't call them pointers*? You know, since they aren't pointers in the computer science sense. The Free On-line Dictionary of Computing defines "pointer": 1. <programming> An address, from the point of view of a programming language. A pointer may be typed, with its type indicating the type of data to which it points. Arithmetic is irrelevant to the definition of "pointer". That's a foible of C, not fundamental to the concept of pointer. Pascal, for example, has pointers too, implemented pretty much in the same way as C/C++, but the type system doesn't allow you to perform arithmetic on them because they aren't treated as integers. Computer science and IT is *dominated* by a single usage for "pointer" -- it's an abstract memory address. The fundamental characteristics of pointers are: - they are first-class values; you can assign a pointer to a variable; - you can dereference a pointer: get the value pointed to; - (in some languages) you can get a pointer to a specific variable (possibly an unnamed, dynamic variable allocated in the heap rather than a named, statically allocated variable). The last two imply that the language must be one where values have fixed addresses, not just as a matter of implementation, but as a matter of language semantics. If they are free to move, they cannot have a fixed address. Python, Java, Ruby, Lua, Javascript etc. have *no such concept* as pointer. There are no values in these languages which correspond to the standard definition of pointer: - you cannot get a pointer to an object or a variable (a name); - since there are no pointers, you cannot dereference them; - or assign them to a variable. Since pointers can be considered an indirect reference to a value, what sort of indirect references does Python have? The simplest thing in Python that is somewhat analogous to a pointer is a *name*, since names allow you to indirectly refer to some value: x = 23 print(x) # prints the value referred to by x, not "x" itself. ptr = "x" # equivalent to "the address of x" y = globals()[ptr] # equivalent to dereferencing Note that names are not first-class values in Python: there is no Name type, and you cannot bind a name to a variable, you have to use a string. It's not a very close analogy, but it's the closest Python has. Implementations of Python, Javascript, Lua, Java, Ruby etc. *may or may not* use pointers in the implementation, but they are not part of the language interface. These languages have no "addressof" operator, no dereference operator, and no "pointer" type; values do not necessarily have fixed addresses (indeed, in Jython and IronPython, values can move in memory). Insisting that Python has pointers is like insisting that you use a text editor by flipping bits. "What happens if I press Ctrl-X?" "Well, these bits on the screen flip from black to white, these bits flip from white to black, and these stay the same." -- Steven -- https://mail.python.org/mailman/listinfo/python-list
