Ian Kelly wrote:
In my view the second one is wrong. a += b should be understood as
being equivalent to a = a + b, but with the *possible* and by no means
guaranteed optimization that the operation may be performed in-place.
This interpretation is at odds with the Language Reference,
section 6.2.1, Augmented Assignment Statements:
"An augmented assignment expression like x += 1 can be rewritten as x = x + 1 to
achieve a similar, but not exactly equal effect... when possible, the actual
operation is performed
in-place, meaning that rather than creating a new object and assigning that to
the target, the old object is modified instead."
Note that it says "when possible", not "if the implementation
feels like it".
In fact, if you read the documentation for lists, you may notice that
while they clearly cover the + operator and the extend method, they do
not explicitly document the list class's += operator.
The "when possible" clause, together with the fact that lists
are mutable, implies that it *will* be done in-place. There
is no need to document all the in-place operators explicitly
for every type.
--
Greg
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