Track variant selectively so reused values round-trip - #360
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`boost::variant` and `std::variant` specialized `tracking_level` to `track_always`. With object tracking on, serializing the same variant twice by value wrote the second occurrence as a bare object reference. On load, that reference could not be resolved into a separate destination: value loads receive their destination by value, not by reference, so the tracking table has nowhere to copy from, and the second variant silently loaded as empty. So, use `track_selectively` (the default for class types) for all three variant flavors: a variant is tracked when serialized through a pointer and stored by value otherwise, matching every other value type. The tracking flag is written per object in the class info, so archives written with the old track_always variant still load correctly and no archive version bump is needed. Also add a regression test that serializes a variant twice into one archive and checks that both copies load back to the original value. Closes #203.
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boost::variantandstd::variantspecializedtracking_leveltotrack_always. With object tracking on, serializing the same variant twice by value wrote the second occurrence as a bare object reference. On load, that reference could not be resolved into a separate destination: value loads receive their destination by value, not by reference, so the tracking table has nowhere to copy from, and the second variant silently loaded as empty.So, use
track_selectively(the default for class types) for all three variant flavors: a variant is tracked when serialized through a pointer and stored by value otherwise, matching every other value type. The tracking flag is written per object in the class info, so archives written with the old track_always variant still load correctly and no archive version bump is needed.Also add a regression test that serializes a variant twice into one archive and checks that both copies load back to the original value.
Closes #203.