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Postings from November 2001
Sam Tregar
# On Thu, 8 Nov 2001, Dan Sugalski wrote:
#
# > Gack. Looks like a mis-placed optimization in perl 5. The
# list of a foreach
# > is *supposed* to flatten at loop start and be static.
# Apparently not. :)
# >
# > Care to file the perl 5 bug report, or shall I?
#
# It's not a bug. Check out the "Foreach Loops" section in
# perlsyn, where
# you'll find:
#
# If any element of LIST is an lvalue, you can modify it by
# modifying VAR inside the loop. Conversely, if any element
# of LIST is NOT an lvalue, any attempt to modify that
# element will fail. In other words, the "foreach" loop
# index variable is an implicit alias for each item in the
# list that you're looping over.
That doesn't support your argument. The point is that in the statement:
foreach(@array) {
...
}
@array should only be evaluated once, at the beginning of the loop. In
effect (using := here, but otherwise Perl 5 code):
my @arraycopy;
for(my $i=0; $i < @array; $i++) {
$arraycopy[$i] := $array[$i];
}
foreach(@arraycopy) {
...
}
except without the actual overhead of having an @arraycopy.
--Brent Dax
brentdax@cpan.org
Configure pumpking for Perl 6
When I take action, I'm not going to fire a $2 million missile at a $10
empty tent and hit a camel in the butt.
--Dubya
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