Patricia tree: Enforce use of smart constructors (fixes bug) #507
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There was a case in `merge'` where we were failing to use the `branch` smart constructor, sometimes causing an invalid branch node where both subtrees were empty. This was causing spurious invariant failures because `equal map1 map2` was false even though both `map1` and `map2` were empty. This fixes the bug, and also tries to prevent future bugs by hiding the `Branch` constructor in a sub-module, enforcing the use of the `branch` smart constructor, which checks each argument for emptiness. Also added `branch_non_empty` to skip the check when the arguments are provably both not empty (for instance, in `add`).
mshinwell
approved these changes
Jun 29, 2021
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There was a case in
merge'where we were failing to use thebranchsmart constructor, sometimes causing an invalid branch node where both
subtrees were empty. This was causing spurious invariant failures
because
equal map1 map2was false even though bothmap1andmap2were empty.
This fixes the bug, and also tries to prevent future bugs by hiding the
Branchconstructor in a sub-module, enforcing the use of thebranchsmart constructor, which checks each argument for emptiness. Also added
branch_non_emptyto skip the check when the arguments are provablyboth not empty (for instance, in
add).