Re^3: Extending a class (corrected)

[Athanasius]

Hello betacentauri,

But I was expecting that, since $self was a MyPackage object, its progeny would be the same species...

Yes, they would be. So within your sub Bar, $self is an instance of class MyPackage; and since MyPackage ISA SVG, $self ISA SVG too.

But don’t be fooled by the names: as far as Perl is concerned, SVG and SVG::Element are separate and unrelated classes! When Perl sees use SVG; (or use parent 'SVG';), it looks for a module named SVG.pm in the directories contained in the global variable @INC. But when it sees use SVG::Element;, it looks in @INC for a directory named SVG, and then within that directory for a module named Element.pm. And that’s it! Apart from their namespaces, the two modules are independent of each other. See perlmod#Packages.

Of course, these classes are related conceptually (i.e., in the programmer’s mind), which is why their author included them both in the SVG distribution (which also contains classes SVG::DOM, SVG::Extension, and SVG::XML); but Perl itself knows nothing of this relationship.

Update: The above is true in the general case. But in this specific case, it turns out that the module SVG.pm actually begins as follows:

package SVG;

use strict;
use warnings;

use SVG::XML;
use parent qw(SVG::Element SVG::Extension);

— so an object of class SVG ISA SVG::Element as well. Thanks to haukex for the heads-up.

Hope that helps,