Re: Accessing class/subclass variables

A big question is what you're using this for. There are a few basic scenarios:

This is a constant that's overridden in each subclass.
Solution: use constant NAME => 'vB'; Then, you say $class->NAME or $obj->NAME and you'll get the right one.

This is a class variable.

Solution: You need a place for class data and a method of accessing it. The simplest way would be something like:

{
    my %data = (
        name => 'vB',
    );

    sub access_class_data {
        my $class = shift;
        my ($name, $val) = @_;

        return $class->SUPER::access_class_data( @_ )
            unless exists $data{ $name };

        if ( @_ > 1 ) {
            $data{ $name } = $val;
        }

        return $data{ $name };
    }
}
[download]

The only drawback is that you have to cut'n'paste this code in every class. Furthermore, you have to pre-seed the items in the %data hash. But, it may be sufficient and it is really simple.

You're conflating class data and instance data.
Solution: Put it in the instance.

My money is on the constant. That's 90% of all class variable usage.

My criteria for good software:

Does it work?
Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

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Re^2: Accessing class/subclass variables by nmerriweather (Friar) on Mar 25, 2006 at 08:46 UTC
It's two class variables - one is a hash, the other is an array of hashes, so sticking them in a constant is messy ( because then its a constant to an anonymous ref , which is a PITA when dereferencing. Both are used by class instances as configuration settings- i glanced at teh code the other day and realized 'hey, with a few more lines i could totally abract these 3 functions into 1' and did. For now, I just stuck a reference to the data in the instance, but i hate doing that with these structures, because now instead of: `sub func(){ my ($self) = @_; foreach my $a (@b){} foreach my $a (keys %c){} }` [download] i have `sub func(){ my ($self) = @_; my @b = @{$self->{'_class_b'}} my %c = %{$self->{'_class_c'}} ... }` [download] which does that annoying coercion into a new array / hash ( i can't just deref and address the needed items, as i need t o loop and nest through them all)	[reply] [d/l] [select]

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Re^2: Accessing class/subclass variables
by nmerriweather (Friar) on Mar 25, 2006 at 08:46 UTC

 sub func(){
  my ($self) = @_;
  foreach my $a (@b){}
  foreach my $a (keys %c){}
 }
[download]

 sub func(){
  my ($self) = @_;
  my @b = @{$self->{'_class_b'}}
  my %c = %{$self->{'_class_c'}}
  ...
 }
[download]

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