Transforming a node causes it to lose external props

[pklavins]

I have an expression tree, in which some nodes have been given extra properties (such as node.depth = 1 or node.priority = 4). However, it seems that putting that expression tree through the transform() function removes those props entirely:

    nodeTree = nodeTree.transform((node) => {
        if (node.priority == priority && node.depth == depth) {
          changed = true;
          return new math.expression.node.ConstantNode(node.eval());
        } else return node;
      });

I even tried embedding the data within the node.comment property, but that gets erased too. I did check the value of node in the else return section and it did contain my added depth and priority props, so something in the transform callback is deleting them.

[josdejong]

Thanks for bringing this up. When transforming a tree, the nodes of the tree are cloned and you will indeed lose any added properties. I think we could either:

1. Introduce a special property attributes (an object) which can be used to put custom data alongside a node, which is neatly copied when cloning the node.
2. When cloning a node, blindly copy all foreign properties that are encountered on the object at hand.

I think I prefer the first solution.

Anyone interested in implementing this?