structuralLookup - API reference

API reference › @evolu/common › Lookup › structuralLookup

function structuralLookup<K>(key: Structural<K>): StructuralLookupKey;

Defined in: packages/common/src/Lookup.ts:380

Returns the structural lookup key for key.

Structural lookup keys are derived from JSON-like values plus Uint8Array. Equal structures produce the same lookup key even when they are different JavaScript instances. undefined values and sparse array holes are rejected rather than skipped.

The derived key is memoized by non-null object identity in a module-scoped WeakMap shared by all callers, so keys must be immutable.

Use this as a Lookup when logical equality should be based on structural value instead of reference identity.

Example

import {
  assertEqual,
  assertSame,
  createLookupMap,
  structuralLookup,
  type StructuralLookupKey,
} from "@evolu/common";

interface Filter {
  readonly table: string;
  readonly where: readonly [string, string];
}

const byFilter = createLookupMap<Filter, string, StructuralLookupKey>({
  lookup: structuralLookup,
});

const cachedFilter: Filter = {
  table: "todo",
  where: ["owner", "ada"],
};
const equivalentFilter: Filter = {
  where: ["owner", "ada"],
  table: "todo",
};
byFilter.set(cachedFilter, "cached");

assertEqual(byFilter.get(equivalentFilter), "cached");
assertSame(byFilter.getKey(equivalentFilter), cachedFilter);

Example

See