SubscriptionRef.modifySomeEffect — API

SubscriptionRef.modifySomeEffectconsteffect/SubscriptionRef.ts:620

<A, B, R, E>(
  modify: (a: A) => Effect.Effect<readonly [B, Option.Option<A>], E, R>
): (self: SubscriptionRef<A>) => Effect.Effect<B, E, R>
<A, B, R, E>(
  self: SubscriptionRef<A>,
  modify: (a: A) => Effect.Effect<readonly [B, Option.Option<A>], E, R>
): Effect.Effect<B, E, R>

Computes a return value and optionally updates the reference effectfully.

When to use

Use to return a separate result while effectfully deciding whether to publish a new SubscriptionRef value.

Details

If the effect succeeds with Option.some, the new value is set and published. If it succeeds with Option.none, the reference is left unchanged and no update is published.

Example (Conditionally modifying with an effect)

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

const program = Effect.gen(function*() {
  const ref = yield* SubscriptionRef.make(10)

  const result = yield* SubscriptionRef.modifySomeEffect(
    ref,
    (n) =>
      Effect.succeed(
        n > 5
          ? (["Updated", Option.some(n + 5)] as const)
          : (["Not updated", Option.none()] as const)
      )
  )
  console.log(result)

  const newValue = yield* SubscriptionRef.get(ref)
  console.log("New value:", newValue)
})

modifications

Source effect/SubscriptionRef.ts:62019 lines

export const modifySomeEffect: {
  <A, B, R, E>(
    modify: (a: A) => Effect.Effect<readonly [B, Option.Option<A>], E, R>
  ): (self: SubscriptionRef<A>) => Effect.Effect<B, E, R>
  <A, B, R, E>(
    self: SubscriptionRef<A>,
    modify: (a: A) => Effect.Effect<readonly [B, Option.Option<A>], E, R>
  ): Effect.Effect<B, E, R>
} = dual(2, <A, B, R, E>(
  self: SubscriptionRef<A>,
  modify: (a: A) => Effect.Effect<readonly [B, Option.Option<A>], E, R>
) =>
  self.semaphore.withPermit(Effect.suspend(() =>
    Effect.map(modify(self.value), ([b, option]) => {
      if (Option.isNone(option)) return b
      setUnsafe(self, option.value)
      return b
    })
  )))