As Randal pointed out, this won't work if the abstract class itself implements stub routines. But it also fails for a bigger reason: At the time you do the can test, the subroutine whose existence you are trying to check has not yet been compiled!

The solution I suggested in the other thread fixes this problem by deferring the check until after compilation is complete. My sample code doesn't deal properly with inherited methods, however. I think a hybrid approach might be effective.

You would use the INIT block approach that I showed, and then in the INIT block, use ->can, and check to see if the returns subroutine was equal to the stub:

sub INIT {
  ...
  my $ref = $inheriting_class->can($method);
  if (! defined($ref)|| 
      defined(&$method) && $ref == \&$method) {
    $bad = 1;
    warn ...;
  }
}

[download]
What is this doing? It tries to resolve the method with $can, the way Ben shows. If there is no such method, that's bad. If there is a method, it then checks to see if there's a stub routine in the abstract class itself, and, if so, if the subclass's method is actually this stub; if so, that's bad too.

You still have the problem with abstract classes that inherit from other abstract classes, of course, but I think solving these problems should be just a SMOP.

In reply to Re: Abstract class methods by Dominus
in thread Interfaces in Perl? by gregorovius

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