Allow builders to return default instance in Java #16655
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rationale: I was investigating allocations during parsing where a lot of empty messages and realized that each of these empty messages was a new instance, when it would be more efficient to reuse the default instance each time. solution: add a default flag to the builder which is invalidated onChange. then conditionally return the default instance if that flag is true.
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rationale: I was investigating allocations during parsing where a lot of empty messages were present and realized that each of these empty messages was a newly allocated instance, when it would be more memory efficient to reuse the default instance each time.
solution: add a default flag to the builder which is invalidated onChange. then conditionally return the default instance if that flag is true.
note: I had to bring back some logic removed in c0d08bd in order for the schema flow to work correctly since it was using toBuilder and expecting a new instance, not the default instance.