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Re: What is the best way to compare variables so that different types are non-equal? (overloading "cmp")

by LanX (Canon)
on Jul 20, 2009 at 01:12 UTC ( #781502=note: print w/ replies, xml ) Need Help??


in reply to What is the best way to compare variables so that different types are non-equal?

Is there a way to override this so that things belonging to different data types are always not equal? Or is the rather verbose (ref($x) eq ref($y)) and ($x eq $y) the only way to do this?

Finally I fiddled it out, the perldoc for overload is not really the lightest weed to smoke. The Regexp object might be magical but still has an API to operate with.

So you may wanna try something like this, but I certainly don't recommend it for production use:

package Regexp; use overload q{cmp} => sub { return 1 if (ref($_[0]) ne ref($_[1])); # TODO: returning 1 is completely arbitrary # didn't know how to decide which ref is "bigger" return "$_[0]" cmp "$_[1]"; }, fallback => 1; ; package main; my $rx = qr/a/; my $ry =qr/a/; my $x="(?-xism:a)"; use Test::More 'tests' => 2; cmp_ok( $rx, 'eq', $ry, '$rx eq $ry'); cmp_ok( $rx, 'ne', $x, '$rx ne $x');

Cheers Rolf


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Re^2: What is the best way to compare variables so that different types are non-equal? (overloading "cmp")
by ikegami (Pope) on Jul 20, 2009 at 08:09 UTC
    Globally changing the behaviour of regex is very wrong. You don't even gain anything from it. The compare function could just as easily be outside of the class.
      Well as I already said
      I certainly don't recommend it for production use
      , a simple comparison function is much easier to maintain. But Beth asked for options with overloading, and thats the answer.

      If one really needs the behavior of a JS-like === very often this could be a way to achieve it. The old behavior of comparing only the stringified values could still be achieved by explicitly stringifying the arguments, e.g.:  "$rx" cmp "$ry".

      IMHO not overloading is the problem in perl5 but the lack of alternative or freely named operators. Actually overloading results in compatibility problems.

      Anyway the fact that it's "a global change of regex" really surprises me, I expected it to be reduced only to the scope of the file...

      Cheers Rolf

        I expected it to be reduced only to the scope of the file...

        There's only one Rexexp package, not one per file.

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