Re: SUBSTR() with replacement or lvalue performance issues

Ilya Zakharevich <nospam-abuse@xxxxxxxxx> wrote:
[A complimentary Cc of this posting was NOT [per weedlist] sent to
Michele Dondi
<bik.mido@xxxxxxxxxxxxx>], who wrote in article
<bs38h49bu6oanughiuvgdgr8rfen2v8fh0@xxxxxxx>:
ISTR that the lvaluedness of substr()'s return value, as long as the
fact that you can EVEN take references of it and modify the string
with a sort of action-at-distance was put there specifically for
performance issues. At some point there were problems with
substitutions having a lenght larger than the substituted IalsoIRC,
but they should be solved in recent enough perls.

See: <http://perlmonks.org/?node_id=498434>

Simple experiments show that it is still buggy with 5.8.8: code below
returns

....


change_nth 7, 'lazy', map{ substr $bigScalar, $_->[0], $_->[1] }
[0,3], [4,5], [10,5], [16,3], [20,5], [26,4], [31,3], [35,4], [40,3];
print "$bigScalar\n";

I don't see this as a bug with substr. "Map" doesn't alias the values
it returns, it copies them. So the magic is no longer there, just as it
isn't present in $x if you do:
my $x=substr $bigScalar, 1, 4;

So if it's a bug, it is a bug with map, not substr.

Xho

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