Graph's root

Components shouldn't be returned out of graph root's Context - unless that's the purpose. They can be translated (mirrored) to different Elements within that graph. When they are passed outside Context of these mirrors, they get resolved to their originals.

Mirrored targets can't keep their mirrored identity outside the graph where they are mirrored. Otherwise
  • the components would need to be mirrored at top-level
    • such global mirrors would affect other graphs, which is against granularity and encapsulation of local Contexts
  • or these Elements would need to be returned by value
    • that creates Element with new identity, so any previous mirrors don't apply to the Element
  • or the graph would have to be deep-copied

Cyclic graphs

TODO
OLD
- When a Mutation can't be referenced as an Element before it's fixed:

ElementShadowed and ElementPure graphs themselves can't be recursive. That's without considering any mirrors. ElementMutants can't create recurrent paths, because a result of mutation can't be referenced before it's fixed. See the reasons below.

Graph of Elements can be cyclic. That requires an ElementContainer which wraps the graph itself. The graph is a mutation of original graph, and it stores a reference to original graph. That's a backward reference. It doesn't involve recursion yet, because it links to old version of the graph and not to the new one. We enclose the graph in an ElementContainer wrapper, which mirrors the old net's root to its mutation. That makes the backward reference point to the new graph. Therefore the resultant net is recursive.
  • lifecycle of ElementMutant implies that graphs of ElementShadowed themselves are never cyclic
    • therefore reference counting can be used for garbage management of ElementShadowed
    • graphs of Elements can be cyclic
  • backward reference
    • reference from within a mutated graph to root of the original graph
    • the reference itself is not recursive
    • when the gate of the mutated graph mirrors the old graph to new one, then the reference becomes recursive
  • gate to a graph
    • Element (or ElementShadowed/ElementPure) which is not a part of the graph. It serves as a handle of that graph.
    • It is a wrapper which keeps mirrors that apply to the whole graph. Usually it translates old graph to its new version. Then a backward reference becomes a recursive link to the current graph.
    • It carries top-level Context of the graph. The graph may become old when passed out of this Context.
    • It is a boundary where the graph should be kept. Visitor mechanism is used to query the graph from outside.

TODO
Recursive objects without graph's gate?


-- Mutation would need to be accessible as Element ( ElementPure with Shadows.EMPTY with Context ) before it is fixed

TODO Mutation's result

-- how to assure that Element counterpart of unfixed Mutation won't be accessed (other than just stored) before it's fixed?
-- multithreading
---- if such Element counterpart is stored in a different thread, then synchronization will need to be used
---- no need for synchronization:
------ 'unfixed' ElementPure will have original, values & mirrors set to null
------ once mutation is fixed, it uses java.reflect.Accessible to set these final null fields
------ it insures that unfixed ElementPure won't make any harm if used as 'fixed', but throws NullPointerException
------ therefore: if unfixed ElementPure is used in a different thread, it's application's responsibility to synchronized it; otherwise it might fail

- Context of unfixed ElementPure
---- MirrorsOwner chains would need to be updated
---- therefore unfixed ElementPure can't be used there
---- that's what ElementPure.fixed field will be for - to check whether the object is fixed
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