# has

Check if a key exists in the Trie.

## Signatures

```ts
export declare const has: {
    (key: string): <V, E, R>(ref: RefTrie<V, E, R>) => RefSubject.Computed<boolean, E, R>;
    <V, E, R>(ref: RefTrie<V, E, R>, key: string): RefSubject.Computed<boolean, E, R>;
};
```

## Why

Makes has a live projection of the trie; consumers can sample it now or observe it without
copying the source state.

## Ownership and lifetime

The has view retains no independent state. An Effect read samples the source once; Fx
observation follows later pushes and its observing Scope owns subscription cleanup.