<A>(self: PubSub<A>): Effect.Effect<number>Returns the current number of messages retained by the PubSub for active
subscribers.
Details
If the PubSub has been shut down, the returned effect succeeds with 0.
The size is not a count of waiting subscribers or suspended publishers.
Example (Getting PubSub size)
import { Effect, PubSub } from "effect"
const program = Effect.gen(function*() {
const pubsub = yield* PubSub.bounded<string>(10)
// Initially empty
const initialSize = yield* PubSub.size(pubsub)
console.log("Initial size:", initialSize) // 0
yield* Effect.scoped(Effect.gen(function*() {
const subscription = yield* PubSub.subscribe(pubsub)
// Publish some messages for the active subscription
yield* PubSub.publish(pubsub, "msg1")
yield* PubSub.publish(pubsub, "msg2")
const afterPublish = yield* PubSub.size(pubsub)
console.log("After publishing:", afterPublish) // 2
yield* PubSub.takeAll(subscription)
}))
})export const const size: <A>(
self: PubSub<A>
) => Effect.Effect<number>
Returns the current number of messages retained by the PubSub for active
subscribers.
Details
If the PubSub has been shut down, the returned effect succeeds with 0.
The size is not a count of waiting subscribers or suspended publishers.
Example (Getting PubSub size)
import { Effect, PubSub } from "effect"
const program = Effect.gen(function*() {
const pubsub = yield* PubSub.bounded<string>(10)
// Initially empty
const initialSize = yield* PubSub.size(pubsub)
console.log("Initial size:", initialSize) // 0
yield* Effect.scoped(Effect.gen(function*() {
const subscription = yield* PubSub.subscribe(pubsub)
// Publish some messages for the active subscription
yield* PubSub.publish(pubsub, "msg1")
yield* PubSub.publish(pubsub, "msg2")
const afterPublish = yield* PubSub.size(pubsub)
console.log("After publishing:", afterPublish) // 2
yield* PubSub.takeAll(subscription)
}))
})
size = <function (type parameter) A in <A>(self: PubSub<A>): Effect.Effect<number>A>(self: PubSub<A>(parameter) self: {
pubsub: PubSub.Atomic<A>;
subscribers: PubSub.Subscribers<A>;
scope: Scope.Closeable;
shutdownHook: Latch.Latch;
shutdownFlag: MutableRef.MutableRef<boolean>;
strategy: PubSub.Strategy<A>;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
}
interface PubSub<in out A>A PubSub<A> is an asynchronous message hub into which publishers can publish
messages of type A and subscribers can subscribe to take messages of type
A.
Example (Publishing and subscribing to messages)
import { Effect, PubSub } from "effect"
const program = Effect.gen(function*() {
// Create a bounded PubSub with capacity 10
const pubsub = yield* PubSub.bounded<string>(10)
// Subscribe and consume messages
yield* Effect.scoped(Effect.gen(function*() {
const subscription = yield* PubSub.subscribe(pubsub)
// Publish messages
yield* PubSub.publish(pubsub, "Hello")
yield* PubSub.publish(pubsub, "World")
const message1 = yield* PubSub.take(subscription)
const message2 = yield* PubSub.take(subscription)
console.log(message1, message2) // "Hello", "World"
}))
})
Companion namespace containing the low-level building blocks used by
PubSub, including atomic implementations, backing subscriptions, replay
windows, and delivery strategies.
PubSub<function (type parameter) A in <A>(self: PubSub<A>): Effect.Effect<number>A>): import EffectEffect.interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<number> => import EffectEffect.const sync: <A>(
thunk: LazyArg<A>
) => Effect<A>
Creates an Effect that represents a synchronous side-effectful computation.
When to use
Use when you need to wrap a synchronous side-effectful operation that is not
expected to throw.
Details
The provided function is evaluated lazily when the effect runs.
Gotchas
The function must not throw. If it throws, the thrown value is treated as a
defect, not as a typed failure. Use try when throwing is expected.
Example (Capturing synchronous logging in an Effect)
import { Effect } from "effect"
const log = (message: string) =>
Effect.sync(() => {
console.log(message) // side effect
})
// ┌─── Effect<void, never, never>
// ▼
const program = log("Hello, World!")
sync(() => const sizeUnsafe: <A>(
self: PubSub<A>
) => number
Returns the current number of messages retained by the PubSub for active
subscribers synchronously.
When to use
Use when an immediate PubSub size snapshot is needed outside effectful code
and concurrent changes between the check and later use are acceptable.
Details
Returns 0 after shutdown. Because this is an unsafe synchronous snapshot,
prefer size in effectful code.
Example (Reading size synchronously)
import { PubSub } from "effect"
// Unsafe synchronous size check
declare const pubsub: PubSub.PubSub<string>
const size = PubSub.sizeUnsafe(pubsub)
console.log("Current size:", size)
sizeUnsafe(self: PubSub<A>(parameter) self: {
pubsub: PubSub.Atomic<A>;
subscribers: PubSub.Subscribers<A>;
scope: Scope.Closeable;
shutdownHook: Latch.Latch;
shutdownFlag: MutableRef.MutableRef<boolean>;
strategy: PubSub.Strategy<A>;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
}