comment on

I'm sure your way is more efficient compared to calling a sub all the time, but I would definitely push for "use constant" in this scenario, especially if you're concerned with efficiency

Suppose the following is in a file called "debug.pl":

*DEBUG = \1;
use constant CONST_DEBUG => 1;
$DEBUG && print "foo\n";
CONST_DEBUG && print "bar\n";
[download]

They look pretty much the same, but you should see the output of perl -MO=Deparse debug.pl

## Output of perl -MO=Deparse on my machine with perl 5.6.1:
*DEBUG=\(1);
sub CONST_DEBUG() {
    package constant;
    $scalar;
}
print "foo\n" if $DEBUG; # <- $DEBUG must be evaluated each time
print "bar\n"; # <- there's no evaluation... just straight print()'ing
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There you see that the second option gives you a literal print "bar\n" without needing to evaluate another variable.

This is because of a couple of reasons: 1 - the perl compiler is smart enough to optimize away "real" constants... and 2 - *DEBUG = \1 is NOT a "real" constant. (You can always assign on top of *DEBUG if you so choose to).

In reply to (lestrrat) Do use 'constant': Re(4): Am I missing something here? by lestrrat
in thread Am I missing something here? by suggus

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