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@zeix/cause-effect

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Cause & Effect - reactive state management primitives library for TypeScript.

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# ADR 0004: isEqual Placement and Deprecation ## Status ✅ Accepted ## Context The `isEqual` deep equality function is used internally for `DEEP_EQUALITY` strategy and was previously exported as part of the public API. During refactoring, a circular import issue arose: - `isEqual` needs access to `CircularDependencyError` (for potential future use) - `CircularDependencyError` lives in `errors.ts` - `errors.ts` already imports from `util.ts` - Therefore, `util.ts` cannot import back from `errors.ts` Additionally, the public export of `isEqual` needed to be addressed as part of API cleanup. ## Decision ### Placement Implementation of `isEqual` in `graph.ts`; public preset exported as `DEEP_EQUALITY` from `graph.ts`. This resolves the circular import issue because: - `graph.ts` already imports `CircularDependencyError` from `errors.ts` - `graph.ts` is the correct home for all equality constants and related functionality - No circular dependency is introduced ### Public Export The deprecated `isEqual` function is re-exported from `index.ts` as a deprecated alias pointing to the implementation in `graph.ts`. This maintains backward compatibility while signaling that the function should not be used going forward. No known downstream consumers exist, but since it was part of the public API, a deprecation cycle is the correct path to removal rather than immediate deletion. ## Alternatives Considered - **Place in `util.ts`**: Blocked — circular import with `errors.ts` - **Keep in `list.ts`**: Rejected — wrong module ownership; `graph.ts` is the natural home - **Remove immediately**: Rejected — breaks deprecation policy; was part of public API ## Consequences - ✅ Resolves circular import constraint - ✅ Maintains API stability through deprecation cycle - ✅ Correct module ownership (equality-related code in `graph.ts`) - ⚠️ Deprecated function remains in public API surface temporarily ## Related - Architecture: [isEqual placement](ARCHITECTURE.md#key-decisions), [isEqual public export](ARCHITECTURE.md#key-decisions) - Requirements: [Minimal Surface, Maximum Coverage](REQUIREMENTS.md#minimal-surface-maximum-coverage)