effect-io-ai

Package: effect
Module: MutableHashMap

MutableHashMap.modify

Updates the value of the specified key within the MutableHashMap if it exists. If the key doesn’t exist, the map remains unchanged.

When to use

Use to transform an existing MutableHashMap value in place without inserting missing keys.

Example (Modifying existing values)

import { MutableHashMap } from "effect"

const map = MutableHashMap.make(["count", 5], ["total", 100])

// Increment existing value
MutableHashMap.modify(map, "count", (n) => n + 1)
console.log(MutableHashMap.get(map, "count")) // Some(6)

// Double existing value
MutableHashMap.modify(map, "total", (n) => n * 2)
console.log(MutableHashMap.get(map, "total")) // Some(200)

// Try to modify non-existent key (no effect)
MutableHashMap.modify(map, "missing", (n) => n + 1)
console.log(MutableHashMap.has(map, "missing")) // false

// Pipe-able version
const increment = MutableHashMap.modify("count", (n: number) => n + 1)
increment(map)

See

• set for inserting or replacing a value directly
• modifyAt for handling both missing and existing keys

Signature

declare const modify: { <K, V>(key: K, f: (v: V) => V): (self: MutableHashMap<K, V>) => MutableHashMap<K, V>; <K, V>(self: MutableHashMap<K, V>, key: K, f: (v: V) => V): MutableHashMap<K, V>; }

Source

Since v2.0.0