# RefTrie.filter

Filter entries into a read-only derived trie.

## Signatures

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

## Why

Creates a read-only Computed trie containing matching entries for current reads and every later
source push; it does not modify the RefTrie.

## Ownership and lifetime

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