CODEWITHSUNDEEP
recursiondata-structuresattributeseiffel
U. Windl
U. Windl

Reputation: 4401

Implementing a common attribute in recursive data type like TREE

When implementing a recursive data structure like TREE, I need a common attribute per TREE, and I wonder how to implement it:

Is there any elegant Eiffel-style solution for that?

Upvotes: 1

Views: 85

Answers (1)

Alexander Kogtenkov
Alexander Kogtenkov

Reputation: 5810

A tree has a distinguished root node that can be used to store information related to the whole tree rather than to a specific node. In order to retrieve this information, there should be a possibility to reach the root node from any other node of the tree. One possible solution is to have a feature parent that would return the parent node of the specified node (or Current for the root). Then, the feature that obtains the root node can look like

root: TREE
        -- The root of the tree.
    local
        p: TREE
    do
        from
            Result := Current
            p := parent
        until
            Result = p -- `Result = Result.parent` when `Result` is root.
        loop
            Result := p
            p := p. parent
        end
    ensure
        Result.parent = Result -- `Result` has no other parent.
    end

Then the tree-specific attribute value can be retrieved from an arbitrary tree node n with n.root.my_attribute.

EDIT:

Another possibility is to have a dedicated CELL with the required data, and all nodes in the tree simply refer to this cell. The benefit is that no reference to the parent node is need and the access to the data is immediate.

Upvotes: 0

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