# RefTrie.keysWithPrefix

Get all keys with a given prefix.

## Signatures

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

## Why

Projects trie state with keys with prefix for both current reads and future pushes, avoiding a
second mutable cache of the derived value.

## Ownership and lifetime

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