effect-io-ai

Package: effect
Module: Ref

Ref.getAndUpdateSome

Gets the current value of the Ref and updates it atomically with the given partial function.

When to use

Use to return the previous Ref value while applying a conditional update.

Details

If the partial function returns Option.some, the Ref is updated with the new value. If it returns Option.none, the Ref is left unchanged. The effect always returns the value that was in the Ref before the attempted update.

Example (Conditionally updating and returning the previous value)

import { Effect, Option, Ref } from "effect"

const program = Effect.gen(function*() {
  const counter = yield* Ref.make(5)

  // Only update if value is greater than 3
  const previous1 = yield* Ref.getAndUpdateSome(
    counter,
    (n) => n > 3 ? Option.some(n * 2) : Option.none()
  )
  console.log(previous1) // 5

  const current1 = yield* Ref.get(counter)
  console.log(current1) // 10

  // Try to update again (won't update since 10 > 3 is true but let's say condition is n < 3)
  const previous2 = yield* Ref.getAndUpdateSome(
    counter,
    (n) => n < 3 ? Option.some(n * 2) : Option.none()
  )
  console.log(previous2) // 10

  const current2 = yield* Ref.get(counter)
  console.log(current2) // 10 (unchanged)
})

See

• getAndUpdate for always applying an update
• updateSome for conditional updates without returning the previous value

Signature

declare const getAndUpdateSome: (<A>(pf: (a: A) => Option.Option<A>) => (self: Ref<A>) => Effect.Effect<A>) & (<A>(self: Ref<A>, pf: (a: A) => Option.Option<A>) => Effect.Effect<A>)

Source

Since v2.0.0