This Perl not compatible with vegetarians:

     package Cow;

     sub new
     {
             my ($this) = shift;
             my ($class) = ref($this) || $this;
             my ($meat) = {};
             bless ($meat, $class);
             return $meat;
     }
 
     sub grind
     {
             my ($meat) = shift;
             bless ($meat, "Beef");
             return $meat;
     }

     package main;

     my ($bessie) = new Cow();

     grind $bessie;
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Certainly you could define a base class for both Cow and Beef which would have methods that both would use (via the @ISA method in the package) so that regardless of the condition of the "$bessie", it is still a member of the base class, even after "grind()".

Where other languages can only "cast" types up the class chain, Perl can make lateral moves, or even a move to left field, as you can re-bless() something at will. Presto!

In your application, I suspect the contents of the object might have to be modified by the conversion method (i.e. grind()) before being re-bless()ed so that the data is compatible with the new methods that it will use.