Re: Readline using foreach and while

Peter J. Holzer wrote:
On 2008-03-27 04:45, szr <szrRE@xxxxxxxxxxxxxxx> wrote:
nolo contendere wrote:
Provably untrue. See Ben's example. I'll restate the concept below.

my @ary = qw/a b c/;
# for (@ary, ()) {
# for ( (), @ary ) {
for ( @ary ) {
push @ary, 'd' if /c/;
print;
}

...

only the uncommented 'for' line prints a 'd' at the end. so what you
say MAY be true if LIST is ONLY an array.

Isn't that because the two commented one are two lists being combined
into a new list, and it's *that* new list that's being iterated
over, so even if you add to @ary, it doesn't change the "new list",
which is just that, a new list created at the start of the loop
before iterating begins - therefore the values of the new list are
set and @ary has nothing to do with it after the create of the "new
list."

Yes. But the same should be true for

for (@ary) {
...
}

for() expects a list, the list is constructed from the elements of
@ary. If you modify @ary after the list is constructed, the list
shouldn't be affected, but it is. I think Ben Morrow is right here:
This smells like an optimization: If there is only a single array, it
can be used directly instead of creating a list from it.

Actually the behaviors of "for (@ary)" and "for (@ary, ())" do seem
consistant if you really think about it. The resulting list is what it
iterates over (from the first element, to what ever *count* is... in the
former case *count* come fro mthe array, and since the condition is
checked at the start of each iteration, if the array is added to, the
count is incremented.

In the latter case, a new list is created from contents of @ary + an
empty list, which gives you a new list, which contains the values of
@ary, but is a new seperate list, and thus is not effected by changes to
@ary because it has it's own copy of @ary's values.

--
szr


.

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