Tuples and immutability

[Gregory Ewing]

Ian Kelly wrote:
> If the in-place behavior of += is held to be part of the interface,
> then we must accept that += is not polymorphic across mutable and
> immutable types,

That's quite correct, it's not. As I said, it's one
notation doing double duty.

Usually there isn't any confusion, because you know
whether any particular instance of it is intended to
operate on a mutable or immutable type.

If that's not the case -- if you're writing a function
intended to operate on a variety of types, some
mutable and some not -- then using in-place operators
would not be appropriate.

> If you want in-place concatenation, the
> obvious way to do it is by calling extend.

It might be the obvious way for that particular operation on
that particular type. But what about all the others?
What's the obvious way to spell in-place set intersection,
for example? (Quickly -- no peeking at the docs!)

The in-place operators provide a standardised spelling
for in-place versions of all the binary operations.
That's a useful thing to have, I think.

-- 
Greg