There are discoveries at every bend on the road to Perl enlightenment. One of the most distracting of these, for me, has been Perl's complex and diverse kinds of namespaces.

I came up with the following simple snippet, when I was experimenting to train myself to recognize (mostly-)namespace gotchas. Seasoned monks may not find this very surprising or interesting, but if you're new as I am, I think it's worth meditating on.

Read this closely:
Updated with comments. 

#!/usr/bin/perl -w
use strict;

package First;
  # set the symbol: MULTIPLIER 
  # and make $x equal to its value.
use constant MULTIPLIER => 5*5;
my $x = MULTIPLIER;

package Second;
  # set a new symbol: if $x is defined in this context,
  # make this MULTIPLIER the same as the first,
  # otherwise "2".
use constant MULTIPLIER => defined $x ? First::MULTIPLIER : 2;
  # easy! It's an error...it's 265...it's 50?  Find out :-)
print MULTIPLIER * $x, "\n";

[download]

Do you know what it will print? Do you know where the values came from?
mkmcconn

UPDATE: I just found this, where tilly shows a very similar behavior.

Update:
tilly it wrapped me in another knot, to add your 

BEGIN{print MULTIPLIER; print "\n";}

[download]
And on the way there, I tried the following with amusing results (which proves tye's point made to me in CB, that the => operator is not just a cute comma: 
BEGIN {print MULTIPLIER => "\n";}

[download]
And then, this from out of left field: 
BEGIN {print MULTIPLIER * sub{return MULTIPLIER}, "\n";}
  # which really ought to be written as below to get 
  # sane results (real obfuscation value there,
  # but not really a namespace issue)
BEGIN {print MULTIPLIER * &{sub{return MULTIPLIER}}, "\n";}

[download]

Hopefully, I wouldn't even think of doing anything like these, in real life. How would you easily know where the whacky numbers are coming from?

In reply to namespace craziness by mkmcconn

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