in reply to overridden method - best way

Your base class should not really have to guess all the future ways in which derived child classes can screw things up :) in the base class, implement the method you want: 

package Parent;
sub X {
   my $self = shift @_;
   print "called Parent::X()\n";
   ...
}
# -------------------
# and in the Child class you specialise this
package Child;
use base qw(Parent)
sub X {
   my $self = shift @_;
   $self->SUPER::X(@_); # Call Base class method
   # then do some extra stuff
   print "called Child::X()\n";
   ...
}
# -------------------
# and further down the chain...
package GrandChild;
use base qw(Child)
sub X {
   my $self = shift @_;
   $self->SUPER::X(@_); # Call up one level
   # then do some extra grandchild stuff
   print "called GrandChild::X()\n";
   ...
}

[download]
This works to any depth of inheritance. One of the main benefits of OO is this type of inheritance where you can specialise a child class without having to recode the Parent and causing unanticipated issues elsewhere.

So in my opinion, _Private_X should be court marshalled. I usually find that $obj->can('method') is more suited for use in handling collections of different types of objects. If you are using it for an inheritance hierarchy trick, look again - its probably a mistake.

Regards,

Jeff

Replies are listed 'Best First'.
Re: Re: overridden method - best way
by jaa (Friar) on May 25, 2004 at 18:02 UTC
    Oh - and a little trick I use to prevent private methods from fooling the inheritance chain... 
    package Parent;
sub X {
   my $self = shift @_;
   print "called Parent::X()\n";
   ...
}
# -------------------
# and in the Child class you specialise this
package Child;
use base qw(Parent)
sub X {
   my $self = shift @_;
   $self->SUPER::X(@_); # Call Base class method

   # local function NOT inherited
   _X($self,@_);

   ...
}
sub _X {
  my $self = shift;
  print "called Child::_X()\n";
}
# -------------------
# and further down the chain...
package GrandChild;
use base qw(Child)
sub X {
   my $self = shift @_;
   $self->SUPER::X(@_); # Call up one level
   # then do some extra grandchild stuff

   # local function NOT inherited
   _X($self,@_);
   ...
}
sub _X {
  my $self = shift;
  print "called GrandChild::X()\n";
}

    [download]

    Note that I do not want the _X() subs called through the inheritance hierarchy, so I call them directly as functions in the current package.

    Regards,

    Jeff

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