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

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Contributed by RiotTown on Mar 29, 2001 at 03:57 UTC
Q&A  > object-oriented programming


Description:

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?

Answer: How do I make a copy constructor? (inheritance?)
contributed by japhy

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

Answer: How do I make a copy constructor? (inheritance?)
contributed by 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.

Answer: How do I make a copy constructor? (inheritance?)
contributed by 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.

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