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variable / @typed/fx

RefSubject.map

Transforms a RefSubject, Computed, or Filtered using a pure function.

Package version
2.0.0-beta.7
Category
Derived queries
Since
1.0.0
Member of
RefSubject

Import

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

Access RefSubject.map through the imported RefSubject 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 map: {
    <T extends RefSubject.Any | Computed.Any | Filtered.Any, B>(f: (a: Success<T>) => B): (ref: T) => T extends Filtered.Any ? Filtered<B, Error<T>, Services<T>> : Computed<B, Error<T>, Services<T>>;
    <A, E, R, B>(ref: RefSubject<A, E, R> | Computed<A, E, R>, f: (a: A) => B): Computed<B, E, R>;
    <A, E, R, B>(filtered: Filtered<A, E, R>, f: (a: A) => B): Filtered<B, E, R>;
    <R0, E0, A, E, R, B, E2, R2>(versioned: Versioned.Versioned<R0, E0, A, E, R, A, E2, R2>, f: (a: A) => B): Computed<B, E0 | E | E2, R0 | R2 | Exclude<R, Scope.Scope>> | Filtered<B, E0 | E | E2, R0 | R2 | Exclude<R, Scope.Scope>>;
};

Why

map creates derived state instead of copying source state into a component. Reads and pushed updates remain connected to the original Versioned value, so a projection can be tested without rendering and consumed by any renderer.

Ownership and lifetime

The returned Computed or Filtered view does not take ownership of the source. It follows the source lifetime and preserves its error and service channels. The pure mapping function adds neither resources nor failures.

Re-computation

The mapping function runs for the current value and subsequent committed source versions. Updates still occur on the writable source; the derived view is read-only unless a more specific bidirectional combinator is used.

Examples

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

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

  // Create a computed that doubles the count
  const doubled = RefSubject.map(count, (n) => 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
})

Other public imports

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

Source