Different immutable versions reuse unchanged component software objects rather than duplicating them. Sharing a linked list suffix or unchanged subtrees saves storage while retaining distinct roots. The shared components must remain immutable for old versions to remain trustworthy. Merely sharing a mutable array does not create a stable snapshot.
Saving references to before/after versions adds constant reference storage per history entry, but the data reachable through those references may be much larger. With balanced-tree path copying, small updates to a size- structure can retain nodes. Whole-array copying can instead retain entries. The implementation and update pattern determine which bound applies.
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