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Efficiently transforms a list of values into a list of Fx streams, using keys to track identity. This is crucial for performance when rendering lists or managing collections of stateful entities. When the input list changes: - New keys cause onValue to be called. - Existing keys have their RefSubject updated with the new value. - Removed keys close the supplied child Scope and clean resources registered through it; the onValue run fiber remains owned by the outer parent Scope.
keyedTick 0. Collections: start.
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.
Each key receives its own RefSubject and child Scope. Reusing a key updates that subject in place. Removing a key closes the child Scope and therefore the resources registered through its supplied Scope service. The onValue run fiber itself is forked in the outer parent Scope, so child-Scope closure does not guarantee interruption of an arbitrary Fx that ignores Scope. Interrupting the outer run closes the parent and remaining children. Source and onValue failures, services, and Scope requirements remain visible in the return type.
Import
import { keyed } from "@typed/fx/Fx";Signatures
export declare const keyed: {
<A, B extends PropertyKey, C, E2, R2>(options: KeyedOptions<A, B, C, E2, R2>): <E, R>(fx: Fx<ReadonlyArray<A>, E, R>) => Fx<ReadonlyArray<C>, E | E2 | Cause.IllegalArgumentError, R | R2 | Scope.Scope>;
<A, E, R, B extends PropertyKey, C, E2, R2>(fx: Fx<ReadonlyArray<A>, E, R>, options: KeyedOptions<A, B, C, E2, R2>): Fx<ReadonlyArray<C>, E | E2 | Cause.IllegalArgumentError, R | R2 | Scope.Scope>;
};Why
A stable key separates identity from position. Consumers can move or update the exact result already associated with a value instead of recreating every result when a collection changes. This is the state-preserving substrate used by keyed template rendering, but the combinator itself is renderer-agnostic.
Ownership and lifetime
Each key receives its own RefSubject and child Scope. Reusing a key updates
that subject in place. Removing a key closes the child Scope and therefore the
resources registered through its supplied Scope service. The onValue run
fiber itself is forked in the outer parent Scope, so child-Scope closure does
not guarantee interruption of an arbitrary Fx that ignores Scope. Interrupting
the outer run closes the parent and remaining children. Source and onValue
failures, services, and Scope requirements remain visible in the return type.
Ordering and failures
Each source array produces a unique-key diff. Added keys start one child Fx;
reused keys update their existing RefSubject, including moves; removed keys
have their child Scope closed. A child may emit repeatedly, replacing only
that key’s latest output. Arrays follow current source order and contain the
contiguous ready prefix: a later key is withheld until every earlier key has
emitted at least once. Debounce coalesces scheduled arrays, not child Fx
values. Duplicate keys fail with Cause.IllegalArgumentError rather than
sharing a child lifetime.
Examples
import { Fx } from "@typed/fx"
const rows = Fx.keyed(Fx.succeed([{ id: "a", value: 1 }]), {
getKey: (row) => row.id,
onValue: (row) => Fx.map(row, ({ value }) => value)
})Other public imports
These import paths expose the same declaration. Each page retains its own public name and signature.