# Fx.switchMap

Maps each element of an Fx to a new Fx, and switches to the latest inner Fx.

When a new element is emitted, the previous inner Fx is cancelled.

## Signatures

```ts
export declare const switchMap: FlatMapLike;
```

## Why

`switchMap` models work whose result becomes obsolete when a newer source
value arrives, such as suggestions for the current query. Cancellation is the
policy: obsolete work is not allowed to finish in the background.

## Switching, ordering, and cardinality

Every source value calls `f`. Before the new inner starts, the previous inner
is interrupted and its interruption is awaited. Only the latest inner remains
active; values it emitted before replacement remain visible, while later
values from the replaced inner are suppressed. There is no result buffer.

## Ownership and lifetime

Source and current-inner failures are forwarded and their services remain
typed. The returned Fx requires `Scope`, which owns the current inner fiber.
Source completion waits for the latest inner. Replacing or interrupting the
output closes obsolete inner work and runs its scoped finalizers before the
replacement proceeds.

## Examples

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

const queries = Fx.mergeAll(
  Fx.at("typed", "0 millis"),
  Fx.at("typed fx", "5 millis")
)
const suggestions = Fx.switchMap(queries, (query) =>
  Fx.ensuring(Fx.at(query, "20 millis"), Effect.log(`${query} closed`))
)
Effect.runPromise(Effect.scoped(Fx.collectAll(suggestions))).then(console.log)
// logs cleanup for "typed" and resolves ["typed fx"]
```