GumpacG opened a new pull request, #3448:
URL: https://github.com/apache/tinkerpop/pull/3448
## Summary
Changes `Tree` from `extends HashMap<T, Tree<T>>` to a `final` class that
holds a `Map` internally and exposes a tree-shaped public API. `Tree` is no
longer a `Map`, which removes inherited `Map` methods whose behavior did
not
align with tree semantics (e.g. `size()` returned root-entry count, not
total
nodes; `containsKey` only checked immediate children).
Per the dev-list discussion:
https://lists.apache.org/thread/o0nqh6kmrkdht531655p351ldjll045d
This is a breaking change targeted at TinkerPop 4.0.0.
## Changes
`Tree` now exposes:
- Navigation: `rootNodes()`, `childAt(key)` (throws if absent),
`hasChild(key)`,
`contains(value)` (recursive), `findSubtree(key)` (recursive,
`Optional`),
`getOrCreateChild(key)` (construction primitive).
- Structure: `isLeaf()`, `nodeCount()`, `getNodesAtDepth(int)`,
`getTreesAtDepth(int)`, `getLeafNodes()`, `getLeafTrees()`.
- Composition/output: `addTree()`, `splitParents()`, `prettyPrint()`,
structural `equals`/`hashCode`/`toString`.
Behavior fixes that fall out of the rewrite:
- `isLeaf()` returns `true` on an empty tree instead of throwing.
- `getNodesAtDepth(0)` returns the root nodes (now 0-based).
Internal callers migrated off the removed `Map` surface:
- `TreeStep` / `TreeSideEffectStep` use `getOrCreateChild` during
construction.
- GraphBinary `TreeSerializer` and GraphSON `TreeJacksonSerializer`/
`Deserializer` (V1–V4) iterate via `rootNodes()`/`childAt()` and rebuild
via
`getOrCreateChild()` + `addTree()`.
- `DetachedFactory` / `ReferenceFactory` gained an explicit `Tree` branch
(previously handled via the `instanceof Map` path).
## Breaking changes
- Code treating a `Tree` as a `Map` (assignment to `Map`, `instanceof Map`,
`get`/`put`/`keySet`/`entrySet`/`size`) no longer compiles.
- Gremlin patterns that worked only because `Tree` was a `Map`
(`select(keys)`,
`count(local)`, `unfold()` on a tree) no longer compose; process the
result
client-side after `next()` or reshape the upstream traversal.
## Speed and Memory
Analytical estimates (not benchmarked); the backing `HashMap` table and
entries
are identical before and after.
- **Memory:** ~16 B more per node — `Tree` now holds a `HashMap` instead of
being one, adding one wrapper object per node. The map itself is
unchanged.
- **Speed:** comparable. Construction is slightly faster
(`getOrCreateChild` is
1–2 map ops vs. the old 3); `childAt` is one op slower (collapsible to
one).
Wire-format encoding is unchanged.
## Testing
- `TreeTest` rewritten against the new API (navigation, recursive
containment/search, depth queries, leaf detection, null keys, structural
equality, `toString`, pretty-print); `TreeSupplierTest` updated.
- `mvn -pl gremlin-core test -Dtest=TreeTest,TreeSupplierTest` passes.
Assisted-by: Kiro: Claude Opus 4.8
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