Class inheriting from class within the namespace

Tree structures are interesting. Often the root of the tree is used as a
handle for the tree itself. However, the tree often has additional
methods beyond that of the root node.

I couldn’t figure out how to do this simply via inheritance due to
chicken-and-egg problems with namespacing:

class Tree < Tree::Node
class Node
end
end
#=> chicken-and-egg.rb:1: uninitialized constant Tree (NameError)

I came up with two alternative techniques to achieve the same goal. I’m
not wild about the way either are handled by RDoc (though the first is
substantially better):

Technique 1: Using modules

class Tree
module NodeStuff
#…all the meat here…
end
include NodeStuff

class Node
  include NodeStuff
end

end

Technique 2: Conjur the chicken first, and kill it later

class TmpTreeNode
# …all the meat here…
end
class Tree < TmpTreeNode
Node = TmpTreeNode
end
Object.class_eval{ remove_const( :TmpTreeNode ) }

Ideally, IMO, Ruby would let me do this:

No “Tree” module or class has yet been defined;

it is a pure namespace at this point

class Tree::Node
# …all the meat here…
end

Now Tree is a class

class Tree < Tree::Node
end

I don’t have any question, and it’s not important enough to me to make
an RCR for the above. I just thought I’d share these thoughts with the
world.

Gavin K. [email protected] wrote:

end
#=> chicken-and-egg.rb:1: uninitialized constant Tree (NameError)

Why wouldn’t you do this?

module TreeStuff
class Node
end
class Tree < Node
end
end

A tree does more than a node (you say), so a tree is a subclass of node
(“a node and then some”). The pair are wrapped up in a module to isolate
their namespace.

Of course I could be missing some other desideratum. m.

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