# RefSubject.mapEffect

Transforms a `RefSubject`, `Computed`, or `Filtered` using an `Effect`ful function.

## Signatures

```ts
export declare const mapEffect: {
    <T extends RefSubject.Any | Computed.Any | Filtered.Any, B, E2, R2>(f: (a: Success<T>) => Effect.Effect<B, E2, R2>): (ref: T) => T extends Filtered.Any ? Filtered<B, Error<T> | E2, Services<T> | R2> : Computed<B, Error<T> | E2, Services<T> | R2>;
    <A, E, R, B, E2, R2>(ref: RefSubject<A, E, R> | Computed<A, E, R>, f: (a: A) => Effect.Effect<B, E2, R2>): Computed<B, E | E2, R | R2>;
    <A, E, R, B, E2, R2>(ref: Filtered<A, E, R>, f: (a: A) => Effect.Effect<B, E2, R2>): Filtered<B, E | E2, R | R2>;
    <R0, E0, A, E, R, E2, R2, C, E3, R3>(versioned: Versioned.Versioned<R0, E0, A, E, R, A, E2, R2>, f: (a: A) => Effect.Effect<C, E3, R3>): Computed<C, E0 | E | E2 | E3, R0 | R2 | R3 | Exclude<R, Scope.Scope>>;
};
```

## Why

Applies one Effectful derivation to current reads and pushed versions. RefSubject and Computed
inputs return Computed and add only `E2`; a Filtered input returns Filtered and preserves its
conditional absence in addition to `E2`.

## Ownership and lifetime

No callback runs until the result is read or observed. Computed results cannot become absent and
do not add `NoSuchElementError`; only the Filtered overload can fail a current read for absence.
Callback services and failures remain `R2` and `E2`, and the observing Scope owns subscription
cleanup.

## Examples

```ts
import { Effect } from "effect"
import * as RefSubject from "@typed/fx/RefSubject"

const program = Effect.gen(function* () {
  const count = yield* RefSubject.make(5)

  // Transform with an async operation
  const doubled = RefSubject.mapEffect(count, (n) =>
    Effect.succeed(n * 2)
  )

  const value = yield* doubled
  console.log(value) // 10

  // Update source
  yield* RefSubject.set(count, 7)

  // Computed automatically updates
  const newValue = yield* doubled
  console.log(newValue) // 14
})
```