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Why is "$A::a" and "$a" diffrent ?
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Why is "$A::a" and "$a" diffrent ? jh3an 03-14-2008
Posted by jh3an on March 14, 2008, 12:38 am
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 The following code doesn't make any sense, does it ?
{
package A;
my $a = 3;
if( ! ($a == $A::a) ){print "not equal\n"}
}

#output will be:
not equal

Why ? I think $A::a equals $a.
If I do not use "my" operator, output will be the one as I expect.

Does "my" operator do something in this case?




Without my operator>>
{
package A;
$a = 3;
if(!($a == $A::a)){print "not equal\n"}
else{ print "equal\n";}
}

#output:
equal



Posted by Ignoramus17007 on March 14, 2008, 1:05 am
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 your my declaration introduced a new $a that is local in scope

> The following code doesn't make any sense, does it ?
> {
> package A;
> my $a = 3;
> if( ! ($a == $A::a) ){print "not equal\n"}
> }
>
> #output will be:
> not equal
>
> Why ? I think $A::a equals $a.
> If I do not use "my" operator, output will be the one as I expect.
>
> Does "my" operator do something in this case?
>
>
>
>
> Without my operator>>
> {
> package A;
> $a = 3;
> if(!($a == $A::a)){print "not equal\n"}
> else{ print "equal\n";}
> }
>
> #output:
> equal
>
>

Posted by Gunnar Hjalmarsson on March 14, 2008, 1:09 am
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jh3an wrote:
> The following code doesn't make any sense, does it ?

Sure it does.

> {
> package A;
> my $a = 3;
> if( ! ($a == $A::a) ){print "not equal\n"}
> }
>
> #output will be:
> not equal
>
> Why ? I think $A::a equals $a.
> If I do not use "my" operator, output will be the one as I expect.
>
> Does "my" operator do something in this case?

It declares the lexically scoped variable $a, which is not the same
variable as the package global $A::a.

> Without my operator>>
> {
> package A;
> $a = 3;
> if(!($a == $A::a)){print "not equal\n"}
> else{ print "equal\n";}
> }
>
> #output:
> equal

In this example, $a is a package global, and $A::a is just the fully
qualified name of the very same variable.

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Posted by Tad J McClellan on March 14, 2008, 7:40 am
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> The following code doesn't make any sense, does it ?
> {
> package A;
> my $a = 3;
> if( ! ($a == $A::a) ){print "not equal\n"}
> }
>
> #output will be:
> not equal
>
> Why ? I think $A::a equals $a.


"Coping with Scoping":

http://perl.plover.com/FAQs/Namespaces.html


--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher0cmdat/"


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