I have an OO parser in two classes Frontend and Backend::Frontend. Frontend inherits from Backend.

Backend parses a file and invokes Frontend::method via a callback for specific chunks of the input document. For instance, it may encounter an element named 'glark', so it calls Frontend::glark($args).

These Frontend methods transform the arguments in some way then either return a string, or recursively call a Backend method to break the input down further. An example of the latter is:

sub Frontend::glark {
  my ($self,$args) = @_;
  return 'glark='.$self->backend_method($args);
}

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This produces the expected output even for complex documents. The problem, I have discovered, is related to the calling of the parent class' methods by Frontend -- the method is invoked correctly, but, as you would expect, the Backend method is invoked on a Backend::Frontend object, which causes no end of problems.

Or, to put it another way:

  1. Backend invokes ($self->{frontend})->frontend_method. (ref($self) eq 'Frontend').
  2. Frontend::frontend_method calls $self->backend_method (intending to dispatch to Backend, as Frontend does a "use base 'Backend'"). (ref($self) eq 'Frontend').
  3. Backend::backend_method is invoked correctly, but now of course ref($self) eq 'Frontend'. Thus, when we do step 1 again later we call the frontend_method of a Frontend object of a Frontend object... This blows up.

I'm sure this problem just represents a basic misunderstanding of Perl OO. I can probably hack around it, but I'd like to know the Right Way. :-)

In reply to OO Parser Class with Callbacks - Confusion by Anonymous Monk

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