note
BrowserUk
<blockquote><i>Oddly enough, the $wheel < 0 may be unnecessary</i></blockquote>
<p>Indeed.
<p>When I originally posted my suggestion, it was purely on the basis of reading the code snippet in the OP. In general, when doing this kind of iteration with a [while] loop, I check the range of the index before attempting to use it to access the array.
<p>Only after [discipulus] refuted the idea, did I download the snippet and play with it and found that as posted, it "worked okay".
<p>It took a little more investigation to understand that it gets away with it because of perl's propensity to accept negative array indices.
<p>The funny thing is, that in one way, coding it "wrongly" has a benefit:<spoiler><code>
#! perl -slw
use strict;
sub incOdo {
my @odo = @_;
my $wheel = $#odo;
# until( $wheel < 0 || $odo[ $wheel ] < 9 ) {
until( $odo[ $wheel ] < 9 || $wheel < 0 ) {
$odo[ $wheel ] = 0;
$wheel--;
}
if( $wheel < 0 ) {
return;
}
else {
$odo[ $wheel ]++;
return @odo;
}
}
my @odo = (0) x 2;
for( 1 .. 102 ) {
print join '', @odo = incOdo( @odo );
}
</code></spoiler>
<ul><li>Coded 'correctly' attempts to iterate beyond the scale of the odometer fail silently:<code>
1
2
3
...
97
98
99
</code>
</li><li>But coded 'wrongly', that beyond range attempt fails noisely:<code>
1
2
3
...
98
99
Use of uninitialized value within @odo in numeric lt (<) at C:\test\junk31.pl line 9.
Use of uninitialized value within @odo in numeric lt (<) at C:\test\junk31.pl line 9.
</code>
<p>which could be seen as an advantage :)
<p>Of course, there are better ways of detecting the failure...
</li></ul>
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