glm-5.1
c9c32a6aa6
Tasks follow the architecture spec phases: - Phase 0: key field on UElement (2 tasks + review) - Phase 1: reactive-host bridge / fiber tree (4 tasks + review) - Phase 2: key-based children reconciliation (3 tasks + review) - Phase 3: unmount & dispose support (4 tasks) - Phase 4: TypeBox value optimizations (4 tasks) Validated with taskgraph CLI: no cycles, 15 parallel generations, 3 high-risk tasks identified (signal-driven-updates, commit-mutations, fiber-disposal).
55 lines
2.2 KiB
Markdown
55 lines
2.2 KiB
Markdown
---
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id: key-matching-algorithm
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name: Key-based old↔new child matching
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status: pending
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depends_on: [review-reactive-host-bridge]
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created: 2026-05-18T16:22:57.216123897Z
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modified: 2026-05-18T16:22:57.216124341Z
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scope: narrow
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risk: medium
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impact: component
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level: implementation
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---
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# Description
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Implement the key-based matching algorithm that maps old children to new children by `key` field. When the tree structure changes (children added, removed, reordered), positional matching is insufficient — it would destroy and recreate instances instead of moving them.
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This algorithm builds two maps from the old and new child lists:
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- `oldKeyMap`: `Map<key | null, Fiber>` — old children keyed by their `key` field (positional fallback for `null` keys)
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- New children are classified as: matched (key exists in old), added (new key), removed (old key not in new)
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For matched children:
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- Same type: will reconcile props (same as Step 2)
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- Type changed: remove old + insert new
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Unkeyed children (key = undefined) fall back to positional matching.
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## Acceptance Criteria
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- [ ] `reconcileChildren` function implemented in `src/host/reconcile.ts`
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- [ ] Builds `oldKeyMap` from existing fiber children
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- [ ] Classifies new children into matched, added, removed sets
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- [ ] Matched children with same type → flag for prop reconciliation
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- [ ] Matched children with different type → old removed, new inserted
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- [ ] Unkeyed children (key = undefined) use positional matching fallback
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- [ ] Duplicate keys: warn and use last-wins (per ADR-004 consequences)
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- [ ] Pure function — no side effects, returns classification for downstream use
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- [ ] New test: keyed children reordered → matched correctly by key
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- [ ] New test: keyed child added at start → old children matched, new child added
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- [ ] New test: keyed child removed → classified as removed
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- [ ] New test: mixed keyed and unkeyed children → key-based for keyed, positional for unkeyed
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- [ ] New test: duplicate key → last-wins, no crash
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## References
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- docs/architecture/reconciler.md — Step 3 (Reconcile Children, Key-Based)
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- docs/architecture/decisions/004-key-as-first-class-field.md — ADR-004, duplicate key behavior
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## Notes
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> To be filled by implementation agent
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## Summary
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> To be filled on completion |