ru...@yahoo.com wrote:
I never claimed that you *couldn't* have copy semantics in C; you can do
almost anything you want in C (or C++). But the *normal* usage of an
array is via a pointer, in which case the semantics are exactly the same
as in Python, Java, REALbasic, .NET, etc.
Arrays are the only datatype in C that don't use
copy-like assignment. Everything else does.
No, arrays are just one reference type; pointers are another (and in
most ways, these are the same thing). When dealing with objects in C++,
one routinely handles them with pointers, so that's the use case which
is analogous to Python -- all the value types can be ignored for the
sake of comparison. (C is not an OOP language, of course, but even
there, all but the most trivial of structs are usually allocated on the
heap and passed around via pointers, just like in C++, Java, .NET, RB,
and Python.)
Ah. OK then, I guess I missed you're point. You're absolutely right;
many languages have both reference types and value types. Python is a
bit unusual in that it has only reference types. I would have picked a
different example to illustrate that, but it's true nonetheless.
If one accepts that there are a "lot" of people
who post in here that clearly are surprised by
Python's assignment semantics, and further appear
to expect assignment to have copy-like semantics,
then where is that expectation coming from?
I think it comes from people stumbling across posts in this forum
claiming that Python has unusual assignment semantics. I wish people
would stop saying that, as it causes a lot of confusion.
How would anyone develop that expectation if (from
a different post in this thread), "[Python's] idea
of assignment is the same as anyone else's."
I can think of two ways:
1. They're new to programming in general, and would have had the same
expectation for any other language. OR,
2. They already understand some other language, and then they come here
and read wild claims that Python's assignment and parameter-passing
semantics are different from other languages. Duped by this claim, they
conclude that, if it's unlike other languages, then Python must have
copy semantics.
If you maintain that reference-like assignment
is very common and something every programmer is
accustomed to, then where are they getting the
copy-like assignment expectations from?
Reference-like assignment IS very common (see
<http://www.strout.net/info/coding/valref/>). So, see above.
I agree that most of the time, when one is using
large (memory) composite "objects", and one needs
to pass, or access them by different names, one will
often use references to do so in order to avoid
expensive copies or to get desired "shared" behavior.
Right.
But (with the exception of C arrays [*1]), doing so
requires some special syntax in all the languages I
mentioned (AFAIK).
Whether you consider it "special" or not, pointers are extremely common
in C. Even more so in C++, which is the closest thing to an OOP
language in the list of moldy languages you mentioned.
You also mentioned VBA -- if that's anything like VB, it does NOT
require any special syntax; a variable is a reference type if its
declared type is a class or string, and a simple type if it's anything
else (just like in .NET, Java, and REALbasic).
So it still seems to me that this is a likely
explanation to why there is frequent misunderstanding
of Python's assignments, and why responding to such
misunderstandings with, "Python's assignments are
the same as other languages'", is at best not helpful.
I don't think so. More likely, people are being confused by the claim
that Python's assignments are NOT like other languages, when in fact
they are.
Best,
- Joe
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