... you should only do this if you are sure that the internal storage is compatible.

As an illustration of this important point, consider:

>perl -wMstrict -le
"use 5.014;
 ;;
 package Foo {
   sub new { return bless { fooble => 'wonkem' }; }
   sub mungeit {
     my $self = shift;
     my ($m) = @_;
     return $self->{fooble} .= $m;
     }
   }
 ;;
 package Bar {
   sub new { return bless { fooble => 1729 }; }
   sub mungeit {
     my $self = shift;
     my ($m) = @_;
     return $self->{fooble} += $m;
     }
   }
 ;;
 my $foo_obj = Foo->new;
 my $bar_obj = Bar->new;
 ;;
 print $foo_obj->mungeit('zoot');
 print $bar_obj->mungeit(42);
 ;;
 bless $foo_obj, 'Bar';
 ;;
 print $foo_obj->mungeit('zonk');
"
wonkemzoot
1771
Argument "zonk" isn't numeric in addition (+) at -e line 1.
Argument "wonkemzoot" isn't numeric in addition (+) at -e line 1.
0
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trizen: In fact, the whole business of re-bless-ing an object into another class is highly suspicious. Is this an instance of an XY Problem? What are you really trying to do?