<A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>Creates a fresh version of this layer that will not be shared.
When to use
Use when you need two parts of an application to receive separate instances of a resource, such as two independent client sessions.
Gotchas
Do not use it just to work around confusing composition. By default, sharing the same layer value is usually the desired behavior.
Example (Creating non-shared layer instances)
import { Context, Effect, Layer, Ref } from "effect"
class Counter extends Context.Service<Counter, {
readonly id: number
}>()("Counter") {}
class Left extends Context.Service<Left, {
readonly counterId: number
}>()("Left") {}
class Right extends Context.Service<Right, {
readonly counterId: number
}>()("Right") {}
const leftLayer = Layer.effect(Left, Effect.gen(function*() {
const counter = yield* Counter
return { counterId: counter.id }
}))
const rightLayer = Layer.effect(Right, Effect.gen(function*() {
const counter = yield* Counter
return { counterId: counter.id }
}))
const showIds = Effect.gen(function*() {
const left = yield* Left
const right = yield* Right
console.log(`same Counter: ${left.counterId === right.counterId}`)
})
const program = Effect.gen(function*() {
const nextId = yield* Ref.make(0)
const counterLayer = Layer.effect(Counter, Effect.gen(function*() {
const id = yield* Ref.updateAndGet(nextId, (n) => n + 1)
console.log("constructed Counter")
return { id }
}))
const shared = Layer.merge(
Layer.provide(leftLayer, counterLayer),
Layer.provide(rightLayer, counterLayer)
)
yield* Effect.provide(showIds, shared)
const freshCounterLayer = Layer.fresh(counterLayer)
const fresh = Layer.merge(
Layer.provide(leftLayer, freshCounterLayer),
Layer.provide(rightLayer, freshCounterLayer)
)
yield* Effect.provide(showIds, fresh)
})
Effect.runPromise(program)
// constructed Counter
// same Counter: true
// constructed Counter
// constructed Counter
// same Counter: falseexport const const fresh: <A, E, R>(
self: Layer<A, E, R>
) => Layer<A, E, R>
Creates a fresh version of this layer that will not be shared.
When to use
Use when you need two parts of an application to receive separate instances
of a resource, such as two independent client sessions.
Gotchas
Do not use it just to work around confusing composition. By default, sharing
the same layer value is usually the desired behavior.
Example (Creating non-shared layer instances)
import { Context, Effect, Layer, Ref } from "effect"
class Counter extends Context.Service<Counter, {
readonly id: number
}>()("Counter") {}
class Left extends Context.Service<Left, {
readonly counterId: number
}>()("Left") {}
class Right extends Context.Service<Right, {
readonly counterId: number
}>()("Right") {}
const leftLayer = Layer.effect(Left, Effect.gen(function*() {
const counter = yield* Counter
return { counterId: counter.id }
}))
const rightLayer = Layer.effect(Right, Effect.gen(function*() {
const counter = yield* Counter
return { counterId: counter.id }
}))
const showIds = Effect.gen(function*() {
const left = yield* Left
const right = yield* Right
console.log(`same Counter: ${left.counterId === right.counterId}`)
})
const program = Effect.gen(function*() {
const nextId = yield* Ref.make(0)
const counterLayer = Layer.effect(Counter, Effect.gen(function*() {
const id = yield* Ref.updateAndGet(nextId, (n) => n + 1)
console.log("constructed Counter")
return { id }
}))
const shared = Layer.merge(
Layer.provide(leftLayer, counterLayer),
Layer.provide(rightLayer, counterLayer)
)
yield* Effect.provide(showIds, shared)
const freshCounterLayer = Layer.fresh(counterLayer)
const fresh = Layer.merge(
Layer.provide(leftLayer, freshCounterLayer),
Layer.provide(rightLayer, freshCounterLayer)
)
yield* Effect.provide(showIds, fresh)
})
Effect.runPromise(program)
// constructed Counter
// same Counter: true
// constructed Counter
// constructed Counter
// same Counter: false
fresh = <function (type parameter) A in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>A, function (type parameter) E in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>E, function (type parameter) R in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>R>(self: Layer<A, E, R>(parameter) self: {
build: (memoMap: MemoMap, scope: Scope.Scope) => Effect<Context.Context<A>, E, R>;
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 Layer<in ROut, out E = never, out RIn = never>A Layer describes how to build one or more services for dependency injection.
When to use
Use to model construction of application services for dependency injection,
especially when services have dependencies, can fail during construction, or
need scoped setup and release.
Details
A Layer<ROut, E, RIn> represents ROut as the services this layer
provides, E as the possible errors during layer construction, and RIn as
the services this layer requires as dependencies.
Layer<function (type parameter) A in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>A, function (type parameter) E in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>E, function (type parameter) R in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>R>): interface Layer<in ROut, out E = never, out RIn = never>A Layer describes how to build one or more services for dependency injection.
When to use
Use to model construction of application services for dependency injection,
especially when services have dependencies, can fail during construction, or
need scoped setup and release.
Details
A Layer<ROut, E, RIn> represents ROut as the services this layer
provides, E as the possible errors during layer construction, and RIn as
the services this layer requires as dependencies.
Layer<function (type parameter) A in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>A, function (type parameter) E in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>E, function (type parameter) R in <A, E, R>(self: Layer<A, E, R>): Layer<A, E, R>R> =>
const fromBuildUnsafe: <ROut, E, RIn>(
build: (
memoMap: MemoMap,
scope: Scope.Scope
) => Effect<Context.Context<ROut>, E, RIn>
) => Layer<ROut, E, RIn>
_: MemoMap(parameter) _: {
get: <RIn, E, ROut>(layer: Layer<ROut, E, RIn>, scope: Scope.Scope) => Effect<Context.Context<ROut>, E, RIn> | undefined;
getOrElseMemoize: <RIn, E, ROut>(layer: Layer<ROut, E, RIn>, scope: Scope.Scope, build: (memoMap: MemoMap, scope: Scope.Scope) => Effect<Context.Context<ROut>, E, RIn>) => Effect<Context.Context<ROut>, E, RIn>;
}
scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}
self: Layer<A, E, R>(parameter) self: {
build: (memoMap: MemoMap, scope: Scope.Scope) => Effect<Context.Context<A>, E, R>;
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; <…;
}
function Layer(memoMap: MemoMap, scope: Scope.Scope): Effect<Context.Context<A>, E, R>build(const makeMemoMapUnsafe: () => MemoMapConstructs a MemoMap synchronously so it can be used to build additional layers.
Example (Creating a memo map unsafely)
import { Context, Effect, Layer } from "effect"
class Database extends Context.Service<Database, {
readonly query: (sql: string) => Effect.Effect<string>
}>()("Database") {}
// Create a memo map for manual layer building
const program = Effect.gen(function*() {
const memoMap = Layer.makeMemoMapUnsafe()
const scope = yield* Effect.scope
const dbLayer = Layer.succeed(Database, {
query: Effect.fn("Database.query")((sql: string) => Effect.succeed("result"))
})
const context = yield* Layer.buildWithMemoMap(dbLayer, memoMap, scope)
return Context.get(context, Database)
})
makeMemoMapUnsafe(), scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}