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Re: Re: namespace craziness

by mkmcconn (Chaplain)
on Jan 30, 2001 at 22:02 UTC ( #55292=note: print w/replies, xml ) Need Help??

in reply to Re: namespace craziness
in thread namespace craziness

Great catch, chipmunk! I see that it is a compile-time issue in the assignment of a value to the constant. Yet, in which namespace is that assignment to $x happening? It's not in "package First" - the $x in the BEGIN block is a global (note no need for use vars: readers could try testing for defined $First::x in the ternary to see what I mean.

What fun! so, let's turn this into a compounded namespace+compile-time (follow the $x) problem, by re-writing the puzzle like this :

#!/usr/bin/perl -w # version chipmunk * .04 use strict; package First; use constant MULTIPLIER => 5*5; my $x = MULTIPLIER / 25; BEGIN {$x = MULTIPLIER}; package Second; use constant MULTIPLIER => defined $x ? First::MULTIPLIER : 2; print MULTIPLIER * $x, "\n"; # now what will it print? __END__

more good points, chipmunk. I think that each element is a red-herring: the special effects of use constant;, my(), and package in these snippets, all highlight how important it is to understand the context of what's happening in the program, where and when. Thanks for your help in thinking through the issues further.

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Re: Re: Re: namespace craziness
by chipmunk (Parson) on Jan 30, 2001 at 22:15 UTC
    $x was declared with my, so it is a lexical variable and not in any namespace/package. The package declarations are really a red herring in this code. Compare these similar scripts:
    #!/usr/bin/perl -w use strict; use constant FIRST => 25; my $x = FIRST; use constant SECOND => defined $x ? FIRST : 2; print SECOND * $x, "\n"; __END__
    #!/usr/bin/perl -w use strict; use constant FIRST => 25; my $x ; BEGIN { $x = FIRST; } use constant SECOND => defined $x ? FIRST : 2; print SECOND * $x, "\n"; __END__

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