How do I make a copy constructor? (inheritance?)

[RiotTown]

I'm fairly new to this perl-OO stuff, but I am making headway except for a recent problem. I've got a package with the follow constructor and accessor methods, but I'm running into problems with creating a copy constructor.

sub new 
{
   my $self;

   $self->{ A } = undef;
   $self->{ B } = undef;

   bless $self, 'Stuff';
}

sub A
{
   my ( $self, $a ) = @_;
   $self->{ A } = $a;
}

---- I've gotten the copy() method below to work:

sub copy
{
   my ( $self ) = @_;
   my ( $new );

   %{ $new } = %{ $self };

   bless $new, 'Stuff';
   return $new;
}

The problem that I'm running into is that in the Stuff object I'd like $self->{ B } to be an array of another type of object (same type of structure, much different data). Whenever I call the copy constructor I just get a reference to the same array as the initial object, not a true copy. Any ideas as to what I'm doing wrong, or am I approaching this the wrong way?

Originally posted as a Categorized Question.

[japhy]

You want a deep copy -- try the Storable module; you want the dclone() function.

[Anonymous Monk]

There is a potential other problem with your code, which I would like to pinpoint as you have talked about inheritance. If your copy method is called for a child of the Stuff class it will generate a Stuff object and not the a Child-Of-Stuff object. In order to avoid this you could bless to ref($self) you might considder it unlikely that a child class will not override the copy constructor, but reasonable applications are thinkable. (e.g.dispatching by class, Stuff is abstract/interface and you just add methods in your child classes etc.) And there is a not OO issue, what if you change the name of your class, you have to change all your bless statements... It is in general a good idea not to hardcode this kind of information.

[Anonymous Monk]

Re: How do I make a copy constructor? (inheritance?)

Originally posted as a Categorized Answer.

[BazB]

merlyn (otherwise known as Randal Schwartz) discusses shallow vs deep copying in one of his columns.

An alternative to Storable for creating clones/copies of objects is the Clone module.