[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [Lookup](https://evolu.dev/docs/api-reference/common/Lookup) › StructuralKey

```ts
type StructuralKey =
  | StructuralScalar
  | ReadonlyArray<StructuralKey>
  | {
      [key: string]: StructuralKey;
    };
```

Defined in: [packages/common/src/Lookup.ts:251](https://github.com/evoluhq/evolu/blob/e7144e2bbe9069362b62dec1b64a8aa922b8f1b0/packages/common/src/Lookup.ts#L251)

Immutable structural key.

Structural keys are JSON-like values with `NaN` and positive/negative
infinity also supported, or `Uint8Array`.

## See

- [Structural](https://evolu.dev/docs/api-reference/common/Lookup/type-aliases/Structural)
- [structuralLookup](https://evolu.dev/docs/api-reference/common/Lookup/functions/structuralLookup)