# RefHashSet.union

Compute the union with another HashSet.

## Signatures

```ts
export declare const union: {
    <V>(that: HashSet.HashSet<V>): <E, R>(ref: RefHashSet<V, E, R>) => Effect.Effect<HashSet.HashSet<V>, E, R>;
    <V, E, R>(ref: RefHashSet<V, E, R>, that: HashSet.HashSet<V>): Effect.Effect<HashSet.HashSet<V>, E, R>;
};
```

## Why

Combines bulk hash set changes in one committed value, giving subscribers one coherent update
rather than a partially applied sequence.

## Ownership and lifetime

Running union performs one serialized hash set transition and resolves with its committed value.
It acquires no resource; failures and services remain those of the source ref.