Lifecycle of Elements

Elements, ElementPures, ElementShadowed, Context and Shadows) are shared accross any number of compound objects. Therefore once in use, they are immutable. That eliminates need for their synchronization. Element fields of ElementContainer are generated on first use - through deferred evaluation, which is thread-safe.

Initially there are only seed Elements. In order to construct new Elements, create an instance of ElementMutant subclass based on given original Element. Once all modifications are committed to ElementMutant, it gets fixed.

Result is available from the start of mutation. However, its fields can't be accessed before the mutation is fixed. That's because its mirrors are not finished yet, and therefore its Context can't be created. Therefore the result can't be passed or returned from any application methods during the mutation. It can be stored in a reference field or be a target of a mirror in another mutation, or even in its own mutation. Inactive Element can't be an original of any mirror. Otherwise an ElementPure could be mirrored within its own Context, or within Context of its components - tricky.

Any access to ElementMutant must be synchronized or locked. ElementMutant can't accept any changes once it is fixed.

ElementMutant subclass can't process any application-specific methods like the ones in Element subclasses. If an active ElementMutant queried its components without returning them out, it would need to wrap them within a Context of that ElementMutant. Such a Context would be changeable while ElementMutant is in use, because its mirrors can be modified.

Reason for Mirrors and Context:

We want to share parts of cyclic graphs among several mutations. That involves mirrors. Mutations without mirrors allow only sharing of:
  • primitive fields
  • tree structures
  • non-cyclic graphs - relaxed trees
    • child nodes can be referred to from several parents
    • no loops
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