Sure, just use bless to change the class.

I don't know why some people seem to be so horrified by this; sometimes it makes sense to do. Specifically, you might want to change the class to implement a conversion method, or upon getting enough information to rebless from a parent, abstract class into a concrete subclass. Depending on your semantics, you may want to maintain the same reference after a conversion, so you don't invalidate references held on to by your clients.

Let me give you an example from my CPAN module Archive::Zip. Here's the inheritance hierarchy, first:

Exporter
  Archive::Zip                        Common base class, has defs.
    Archive::Zip::Archive             A Zip archive.
    Archive::Zip::Member              Abstract superclass for all memb
+ers.
      Archive::Zip::StringMember      Member made from a string
      Archive::Zip::FileMember        Member made from an external
file
      Archive::Zip::ZipFileMember     Member that lives in a zip file
      Archive::Zip::NewFileMember     Member whose data is in a file
      Archive::Zip::DirectoryMember   Member that is a directory
[download]

So far so good. I re-bless objects in a couple of instances. To do this, I have an inherited method called _become:

# Morph into given class (do whatever cleanup I need to do)
sub _become # Archive::Zip::Member
{
 return bless( $_[0], $_[1] );
}
[download]

This is overridden in the various member classes to add cleanup (that is, remove subclass-specific data, seek file handles to safe places, and call the SUPER::_become). For instance:

sub _become # Archive::Zip::FileMember
{
 my $self = shift;
 my $newClass = shift;
 return $self if ref( $self ) eq $newClass;
 delete( $self->{'externalFileName'} );
 delete( $self->{'fh'} );
 return $self->SUPER::_become( $newClass );
}
[download]

Where is this used? One of the places is in the routine that reads a Zip file. There is a loop that reads members from the file. These are initially created as Archive::Zip::ZipFileMember. But in the case of directories, there's no actual data, and we want an Archive::Zip::DirectoryMember instead. So the members that represent directories get changed to the DirectoryMember class.

The other place where the re-blessing happens is when someone changes the contents of a member by passing in a string. Since most of the data in the object is correct, and since clients may have references to the existing member, I just change the member (which may be of any member type) to an Archive::Zip::StringMember (if it isn't already).

Anyway, depending on the use of your objects, it may make sense. But I wouldn't do it before I did a pretty rigorous analysis of my object model.

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