# mapError

Map the error value of a RefResult.

## Signatures

```ts
export declare const mapError: {
    <ResultE, ResultE2>(f: (e: ResultE) => ResultE2): <A, Err, R>(ref: RefResult<A, ResultE, Err, R>) => RefSubject.Computed<Result.Result<A, ResultE2>, Err, R>;
    <A, ResultE, Err, R, ResultE2>(ref: RefResult<A, ResultE, Err, R>, f: (e: ResultE) => ResultE2): RefSubject.Computed<Result.Result<A, ResultE2>, Err, R>;
};
```

## Why

Projects result state with map error for both current reads and future pushes, avoiding a second
mutable cache of the derived value.

## Ownership and lifetime

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