Node policy

If a field is not marked with to.field the following policy will be applied when determining whether a field is a node or not:

• If the field is annotated with a Tree subtype or a generic containing a Tree subtype e.g. List[to.Tree], the field is considered a node.
• If the runtime value of the field is a to.Tree instance, the field is considered a node. The Tree's metadata will be updated to reflect this.
• If none of the above apply, the field is considered a static field.

import treeo as to

class Agent(to.Tree):
    ...

class Game(to.Tree):
    player: Agent      # node
    cpus: List[Agent]  # node
    max_cpus: int      # static

    def __init__(self, ...):
        ...
        self.boss = Agent(...) # runtime node

Note: the kind of all fields that are not explicitly declarated is set to NoneType.