mce has asked for the wisdom of the Perl Monks concerning the following question:

Hi All,

There are many posts about the magic of sort.

I have a question that -I think- isn't handled before.

Last week, I found that the result of my code was not correct, and after digging deep in my code, I found that the problem was a typo, as I have written cmp instead of <=>.

This bug is one of the hardest to find as the perl code runs OK.

Now, when warnings are on, perl complains that the following code is wrong.

perl -W -e 'warn sort {$a <=> $b} qw(A B);'
but this isn't.
perl -W -e 'warn sort {$a cmp $b} qw(1 2);'
Wouldn't it be possible to alter perl so that it complains when using cmp when comparing only numbers?
At least, I would think this is very usefull.
I don't know that much about the perl internals, but I guess it must be doable.
Dr. Mark Ceulemans
Senior Consultant
BMC, Belgium