Search documentation

Search by topic, API name, or import path.

GitHub ↗

variable / @typed/fx

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.

Package version
2.0.0-beta.7
Category
Concurrent work
Since
1.0.0
Member of
Fx

Follow one execution

b interrupts pending a; only b finishes and emits.

Fx timelineswitchMapEffect(preview)switchMapEffect
OperatorswitchMapEffect(preview)
Read this diagram

Follow each lane from left to right. Events stacked vertically share a tick; the green cursor marks the current time across every lane.

  • A value
    The text inside the pill is the emitted value.
  • Work starts
    The raised chevron starts an inner run (^ in the source).
  • The run returns
    The vertical bar ends this lane’s run.
  • A cause is delivered
    The exclamation mark belongs to this lane.
  • Work is interrupted
    The cross marks cancellation of this run.
  • Current time
    The line and diamond move together across all lanes.
  • Happening now
    A highlighted event is at the current tick.
  • Still ahead
    Muted, dashed values have not happened yet.
  • Time continues
    The lane’s arrow is not a return marker. An empty stretch can be quiet work that is still running.

Illustrated ticks start at 0. At 1×, one illustrated tick takes one second; captions specify real durations when timing matters. A cause or interruption belongs to its lane, and other work may continue. Scroll horizontally to inspect the rest of a long timeline.

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.

Source implementation · Learn the surrounding model

Compare all Fx timelines →

Import

import { Fx } from "@typed/fx";

Access Fx.switchMapEffect through the imported Fx export. Its declaration below describes the member.

This public exposure is a re-export. Its import path is supported; declaration documentation is shared with the other public exposures below.

Signatures

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

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"]

Other public imports

These import paths expose the same declaration. Each page retains its own public name and signature.

Source