Dear monks,

I have a whole bunch of different objects; for example "node" objects, which can go into a "tree" object, which can go into a "trees" (note: plural) object. The underlying data structures for the "tree" and "trees" objects are array refs. Likewise, I also have "datum" objects, which go into a "matrix" object, which go into a "matrices" object. Again, the "matrix" and "matrices" objects are blessed anonymous array refs.

Now, all objects that are blessed array refs inherit from the abstract "listable" object, which has a bunch of methods that are handy for array-like structures (for example filters, where you loop through all entities in the array and return all entities that meet a certain condition). I also want to be able to have a listable method "insert", with the following behaviour: 
$tree->insert($node); #works

$matrix->insert($datum); #works

$trees->insert($node); #error: $trees object can't contain $node

$matrix->insert($node); #error: $matrix object can't contain $node

[download]
Also, I want this Listable::insert method to have the following properties: ...so that the method also works for "specialnode" objects that inherit from the "node" object (for example).

Here's what I did to achieve this: all objects have two methods that return strings to indicate i) what "container_type" the object is; ii) what type of "container" it can be inserted into. Then, internally, the Listable::insert method becomes sort of like this: 
sub insert {
    my ( $self, $obj_to_insert ) = @_;
    if ( $self->container_type eq $obj_to_insert->container ) {
        push(@{$self}, $obj_to_insert);
    }
    else {
        die "I can't hold that object!";
    }
}

[download]
The downside of this is that every insertion involves two method calls and a string comparison. Also, it feels a bit hokey, I think.

So now my question: can anyone recommend a more elegant and efficient way to achieve the same behaviour?

Thanks!

In reply to "polymorphism" hack: nuts or wise? by rvosa

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