Skip to main content Link Search Menu Expand Document (external link)
effect-extras

MapX overview

Generic, framework-agnostic extensions for working with Map.

Added in v0.0.0

Table of contents

combinators

getOrElseSetGet

Like Map.prototype.get, but when the key is absent it stores the computed fallback at that key and returns it. Mutates the input map in place.

Use it for memoization-style caches where a miss should both populate the map and yield the value in one step. Throws if the resolved value is nullish (only possible when fallbackIfNotFound returns null/undefined for a value type that admits them — treated as a programmer error). Supports both data-first and data-last (pipeable) call styles.

Signature

export declare const getOrElseSetGet: (<K, V>(key: K, fallbackIfNotFound: () => V) => (map: Map<K, V>) => V) &
  (<K, V>(map: Map<K, V>, key: K, fallbackIfNotFound: () => V) => V)

Example

import { MapX } from "@nunofyobiz/effect-extras"
import { pipe } from "effect"

// Miss: stores the fallback and returns it (data-first)
const map = new Map<string, number>()
assert.deepStrictEqual(
  MapX.getOrElseSetGet(map, "a", () => 1),
  1
)
assert.deepStrictEqual(map.get("a"), 1)

// Hit: returns the existing value, fallback is ignored (data-last)
assert.deepStrictEqual(
  pipe(
    map,
    MapX.getOrElseSetGet("a", () => 99)
  ),
  1
)

Added in v0.0.0