# Fx.switchMapEffect

Maps each element of an Fx to an Effect, and switches to the latest effect.

When a new element is emitted, the previous effect is cancelled.

## Signatures

```ts
export declare const switchMapEffect: FlatMapEffectLike;
```

## Why

This is the Effect-producing form of {@link switchMap }. It makes latest-only
Effect execution explicit without wrapping callbacks with `Fx.fromEffect`.

## Switching and cardinality

Every source value creates one callback Effect. A new value interrupts and
awaits the previous Effect before starting its replacement. Each Effect can
emit one successful result, but an interrupted Effect may emit none.

## Ownership and lifetime

Source and current callback failures remain typed and callback services are
added to requirements. The required `Scope` owns the current Effect. Source
completion waits for it; replacement and output interruption run its
finalizers before relinquishing the lifetime.

## Examples

```ts
import { Fx } from "@typed/fx"
import { Effect } from "effect"

const queries = Fx.mergeAll(
  Fx.at("a", "0 millis"),
  Fx.at("ab", "5 millis")
)
const result = Fx.switchMapEffect(queries, (query) =>
  Effect.as(Effect.sleep("20 millis"), query).pipe(
    Effect.ensuring(Effect.log(`${query} closed`))
  )
)
Effect.runPromise(Effect.scoped(Fx.collectAll(result))).then(console.log)
// ["ab"]
```