On Wednesday, 16 May 2012 at 21:40:39 UTC, Andrei Alexandrescu
wrote:
On 5/16/12 4:37 PM, Nick Sabalausky wrote:
One counter-argument that was raised is that TDPL has an
example on page 381
that indicates foreach iterates over an implicit copy. I don't
have a copy
handy ATM, so I can't look at it myself, but I'd love to see
Andrei weigh in
on this: I'm curious if this example in TDPL made that copy
deliberately, or
if the full implications of that copy were just an oversight.
It is deliberate and the intent is that millions of programmers
used to foreach from other languages don't scream "where is my
range???"
Andrei
According to the docs, however, an InputRange that is not a
ForwardRange won't necessarily behave the way millions of
programers used to foreach from other languages expect them to.
Such an operation will most likely consume the underlying data,
whether foreach makes an implicit copy or not.
Put another way, whether a non-ForwardRange is consumed by a
foreach the way it currently works is unspecified.
The docs also say that the right way to checkpoint a ForwardRange
is by calling save().
This tells me that the most intuitive way for foreach to work is:
a. If it's a ForwardRange, make a copy with save(), then consume
the copy.
b. If it's not a ForwardRange, consume the original.
