Here's a thought on implementing "abstract" classes in Perl, should you decide that you want to.

One thing that distinguishes an "abstract" class from a concrete one is that you shouldn't create instances the abstract class. There's no need for special syntax for this. You need merely do something like: 

    package AbstactFoo;
    ...
    sub new {
        die "Don't create any Abstract Foos direct, fool!";
    }

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And then rely on subclasses to implement their own new. Unfortunately, this confounds the common (and useful) idiom of inheriting new from a (possibly abstract) superclass. 
   package AbstractFoo;
    ...
    sub new {
        my $package = shift;
        bless { @_ }, $package;
    }
    ...
    my $foo1 = new SubclassOfAbstractFoo(); # GOOD
    my $foo2 = new AbstractFoo();           # BAD

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Here's a way to get the benifit of an "abstract" new while still keeping the class abstract: 
    package AbstractFoo;
    ...
    sub new {
        my $package = shift;
        die "Don't subclass AbstractFoo directly!"
           if $package eq "AbstractFoo";
        bless { @_ }, $package;
    }

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(Bonus points to whoever sees a way to generalize this even further.)

In reply to Re: Why do you need abstract classes in Perl? by dws
in thread Why do you need abstract classes in Perl? by jeffa

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