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Answer: How do I create static class variables (class data)?

by btrott (Parson)
on Apr 21, 2000 at 03:38 UTC ( #8300=categorized answer: print w/replies, xml ) Need Help??

Q&A > object-oriented programming > How do I create static class variables (class data)? - Answer contributed by btrott

Perl doesn't have a special syntax for creating such variables. All you have to do, basically, is declare a lexical variable at the start of the file in which you're declaring your class, like
package Foo; my $Bar = 0;
It's important to declare it with my rather than as a package global, because the latter could be accessed directly by scripts using your class--and you don't want that (well, most likely you don't).

You shouldn't just use this variable directly in your class, though, because your class won't be very inheritable. Subclasses that inherit your methods will be altering *your* class variable rather than their own; you don't want this.

To fix this, take a reference to the data and store it in your objects. For example, say that you have an object that's really a hash reference--to give it access to your class data, you could do this:

$self->{'_BAR'} = \$Bar;
in your constructor. When you want to access the class data, then, just use it like you would a regular reference:
print "\$Bar is currently ", ${ $self->{'_BAR'} };
And there you go! Your very own static member.

For more information and for some practical uses of such a variable, take a look at perltoot.

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