effect-io-ai

Package: effect
Module: HashMap

HashMap.modifyAt

Sets or removes the specified key using an update function.

Details

The update function receives Some(value) when the key exists or None when it does not. Returning Some(newValue) stores the value, and returning None removes the key or leaves it absent.

Example (Updating values with Options)

import { HashMap, Option } from "effect"

const map = HashMap.make(["a", 1], ["b", 2])

// Increment existing value or set to 1 if not present
const updateFn = (option: Option.Option<number>) =>
  Option.isSome(option) ? Option.some(option.value + 1) : Option.some(1)

const updated = HashMap.modifyAt(map, "a", updateFn)
console.log(HashMap.get(updated, "a")) // Option.some(2)

Signature

declare const modifyAt: { <K, V>(key: K, f: HashMap.UpdateFn<V>): (self: HashMap<K, V>) => HashMap<K, V>; <K, V>(self: HashMap<K, V>, key: K, f: HashMap.UpdateFn<V>): HashMap<K, V>; }

Source

Since v2.0.0