Shlomi Fish <shlo...@shlomifish.org> writes:
> Hi Lee,
>
> On Wed, 26 Jun 2013 10:18:44 +0200
> lee <l...@yun.yagibdah.de> wrote:
>
>> Hi,
>>
>> the following example doesn't compile:
>>
>>
>> use strict;
>> use warnings;
>>
>>
>> sub test {
>> print $counter . "\n";
>> }
>>
>>
>> my $counter = 0;
>> while($counter < 5) {
>> test();
>> $counter++;
>> }
>>
>>
>> It says "Global symbol "$counter" requires explicit package name ...".
>> When I put the subroutine after the 'while' loop, it works just fine, so
>> what's the problem?
>
> The subroutine does not see the lexical $counter variable because it was
> declared after its scope.
The subroutine is never called before $counter is declared, so it is
always available to the subroutine. There should be an error only for
instances when the subroutine is called before $counter is declared.
> For more information, see:
>
> * http://www.plover.com/FAQs/Namespaces.html
Ok, so perl has a totally broken design with variables :( What's the
solution to this problem? I do not want to:
+ define the subroutines after the program
+ carry the needed variables all over the place as parameters to every
function that might need it
+ declare the variables on top of the program because that increases
their scope too much
Reading [1] would indicate that it is an extremely bad idea in perl to
have global (package) variables because they cannot be local to the
program that uses them because all programs are packages the variables
of which can be accessed from other packages. You also cannot use a
package name and use that for variables like $Mypackage::counter because
in case you ever change the name of the package, you'll have to go
through all the code and adjust the names of such variables. It
wouldn't really solve the problem, either, because the variables could
still be accessed from outside the program. So now I don't want to have
global (package) variables, either.
In the particular application I have this problem with, I could create a
hash holding all the information that might be needed by subroutines and
carry that all over the place in their parameters. In C, I would create
a structure containing the needed information and simply carry a pointer
to the structure. That would be much more efficient than handing over a
hash, effectively copying all the data the hash may contain every time.
How do you do that in perl?
[1]: http://www.plover.com/FAQs/Namespaces.html
--
"Object-oriented programming languages aren't completely convinced that
you should be allowed to do anything with functions."
http://www.joelonsoftware.com/items/2006/08/01.html
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