<X, E, R>(effect: Effect<X, E, R>): Layer<
never,
E,
Exclude<R, Scope.Scope>
>Constructs a layer from an effect, discarding its value and providing no services.
When to use
Use when layer construction should run an Effect for its side effects while providing no services.
Example (Running an effect during layer construction)
import { Effect, Layer } from "effect"
const initLayer = Layer.effectDiscard(
Effect.sync(() => {
console.log("Initializing application...")
})
)export const const effectDiscard: <X, E, R>(
effect: Effect<X, E, R>
) => Layer<never, E, Exclude<R, Scope.Scope>>
Constructs a layer from an effect, discarding its value and providing no
services.
When to use
Use when layer construction should run an Effect for its side effects while providing no
services.
Example (Running an effect during layer construction)
import { Effect, Layer } from "effect"
const initLayer = Layer.effectDiscard(
Effect.sync(() => {
console.log("Initializing application...")
})
)
effectDiscard = <function (type parameter) X in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>X, function (type parameter) E in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>E, function (type parameter) R in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>R>(effect: Effect<X, E, R>(parameter) effect: {
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; <…;
toString: () => string;
toJSON: () => unknown;
}
import EffectEffect<function (type parameter) X in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>X, function (type parameter) E in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>E, function (type parameter) R in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>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<never, function (type parameter) E in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>E, type Exclude<T, U> = T extends U
? never
: T
Exclude from T those types that are assignable to U
Exclude<function (type parameter) R in <X, E, R>(effect: Effect<X, E, R>): Layer<never, E, Exclude<R, Scope.Scope>>R, import ScopeScope.Scope>> =>
const effectContext: <A, E, R>(
effect: Effect<Context.Context<A>, E, R>
) => Layer<A, E, Exclude<R, Scope.Scope>>
Constructs a layer from an effect that produces all services in a Context.
When to use
Use when you need a Layer that effectfully constructs a Context with
multiple services.
Details
This allows you to create a Layer from an effectful computation that
returns multiple services. The Effect is executed in the scope of the
layer.
Example (Creating a layer from an effectful context)
import { Context, Effect, Layer } from "effect"
class Database extends Context.Service<
Database,
{ readonly query: (sql: string) => Effect.Effect<string> }
>()("Database") {}
const layer = Layer.effectContext(
Effect.succeed(Context.make(Database, {
query: (sql: string) => Effect.succeed(`Query: ${sql}`)
}))
)
effectContext(import internalEffectinternalEffect.const as: {
<A, B>(value: B): <E, R>(
self: Effect.Effect<A, E, R>
) => Effect.Effect<B, E, R>
<A, E, R, B>(
self: Effect.Effect<A, E, R>,
value: B
): Effect.Effect<B, E, R>
}
effect: Effect<X, E, R>(parameter) effect: {
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; <…;
toString: () => string;
toJSON: () => unknown;
}
import ContextContext.empty()))