zopu-code/repos/effect-smol/migration/runtime.md

Runtime: Runtime<R> Removed

In v3, Runtime<R> bundled a Context<R>, RuntimeFlags, and FiberRefs into a single value used to execute effects:

// v3
interface Runtime<in R> {
  readonly context: Context.Context<R>
  readonly runtimeFlags: RuntimeFlags
  readonly fiberRefs: FiberRefs
}

In v4, this type no longer exists and you can use Context<R> instead. Run functions live directly on Effect, and the Runtime module is reduced to process lifecycle utilities.

Runtime.runFork(runtime) -> Effect.runForkWith(services)

In v3, running an effect with dependencies usually meant pulling the current runtime from Effect.runtime<R>() and calling Runtime.runFork(runtime) inside the main effect.

v3

import { Context, Effect, Runtime } from "effect"

class Logger extends Context.Tag("Logger")<Logger, {
  readonly log: (message: string) => void
}>() {}

const program = Effect.gen(function*() {
  const logger = yield* Logger
  logger.log("Hello from Logger")
})

const main = Effect.gen(function*() {
  const runtime = yield* Effect.runtime<Logger>()
  return Runtime.runFork(runtime)(program)
}).pipe(
  Effect.provideService(Logger, {
    log: (message) => console.log(message)
  })
)

const fiber = Effect.runFork(main)

In v4, use the same pattern with Effect.context<R>(), then run with Effect.runForkWith(services):

v4

import { Context, Effect } from "effect"

class Logger extends Context.Service<Logger, {
  readonly log: (message: string) => void
}>()("Logger") {}

const program = Effect.gen(function*() {
  const logger = yield* Logger
  logger.log("Hello from Logger")
})

const main = Effect.gen(function*() {
  const services = yield* Effect.context<Logger>()
  return Effect.runForkWith(services)(program)
}).pipe(
  Effect.provideContext(Context.make(Logger, {
    log: (message) => console.log(message)
  }))
)

const fiber = Effect.runFork(main)

If your effect has no service requirements, use Effect.runFork(effect).

Runtime Module Contents

The Runtime module now only contains:

• Teardown — interface for handling process exit
• defaultTeardown — default teardown implementation
• makeRunMain — creates platform-specific main runners