<I, S>(service: Context.Key<I, S>): <E, R>(
effect: Effect<S, E, R>
) => Layer<I, E, Exclude<R, Scope.Scope>>
<I, S, E, R>(
service: Context.Key<I, S>,
effect: Effect<Types.NoInfer<S>, E, R>
): Layer<I, E, Exclude<R, Scope.Scope>>Constructs a layer from an effect that produces a single service.
When to use
Use when you need to construct a Layer-provided service with an Effect,
dependencies, or scoped resource acquisition.
Details
This allows you to create a Layer from an Effect that produces a service.
The Effect is executed in the scope of the layer, allowing for proper
resource management.
Example (Creating a layer from an effect)
import { Context, Effect, Layer } from "effect"
class Database extends Context.Service<Database, {
readonly query: (sql: string) => Effect.Effect<string>
}>()("Database") {}
const layer = Layer.effect(Database,
Effect.sync(() => ({
query: (sql: string) => Effect.succeed(`Query: ${sql}`)
}))
)export const const effect: {
<I, S>(service: Context.Key<I, S>): <E, R>(
effect: Effect<S, E, R>
) => Layer<I, E, Exclude<R, Scope.Scope>>
<I, S, E, R>(
service: Context.Key<I, S>,
effect: Effect<Types.NoInfer<S>, E, R>
): Layer<I, E, Exclude<R, Scope.Scope>>
}
Constructs a layer from an effect that produces a single service.
When to use
Use when you need to construct a Layer-provided service with an Effect,
dependencies, or scoped resource acquisition.
Details
This allows you to create a Layer from an Effect that produces a service.
The Effect is executed in the scope of the layer, allowing for proper
resource management.
Example (Creating a layer from an effect)
import { Context, Effect, Layer } from "effect"
class Database extends Context.Service<Database, {
readonly query: (sql: string) => Effect.Effect<string>
}>()("Database") {}
const layer = Layer.effect(Database,
Effect.sync(() => ({
query: (sql: string) => Effect.succeed(`Query: ${sql}`)
}))
)
effect: {
<function (type parameter) I in <I, S>(service: Context.Key<I, S>): <E, R>(effect: Effect<S, E, R>) => Layer<I, E, Exclude<R, Scope.Scope>>I, function (type parameter) S in <I, S>(service: Context.Key<I, S>): <E, R>(effect: Effect<S, E, R>) => Layer<I, E, Exclude<R, Scope.Scope>>S>(service: Context.Key<I, S>(parameter) service: {
Identifier: Identifier;
Service: Shape;
key: string;
stack: string | undefined;
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.type Context.Key = /*unresolved*/ anyKey<function (type parameter) I in <I, S>(service: Context.Key<I, S>): <E, R>(effect: Effect<S, E, R>) => Layer<I, E, Exclude<R, Scope.Scope>>I, function (type parameter) S in <I, S>(service: Context.Key<I, S>): <E, R>(effect: Effect<S, E, R>) => Layer<I, E, Exclude<R, Scope.Scope>>S>): <function (type parameter) E in <E, R>(effect: Effect<S, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>E, function (type parameter) R in <E, R>(effect: Effect<S, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>R>(
effect: Effect<S, 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) S in <I, S>(service: Context.Key<I, S>): <E, R>(effect: Effect<S, E, R>) => Layer<I, E, Exclude<R, Scope.Scope>>S, function (type parameter) E in <E, R>(effect: Effect<S, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>E, function (type parameter) R in <E, R>(effect: Effect<S, E, R>): Layer<I, 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<function (type parameter) I in <I, S>(service: Context.Key<I, S>): <E, R>(effect: Effect<S, E, R>) => Layer<I, E, Exclude<R, Scope.Scope>>I, function (type parameter) E in <E, R>(effect: Effect<S, E, R>): Layer<I, 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 <E, R>(effect: Effect<S, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>R, import ScopeScope.Scope>>
<function (type parameter) I in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>I, function (type parameter) S in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>S, function (type parameter) E in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>E, function (type parameter) R in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>R>(
service: Context.Key<I, S>(parameter) service: {
Identifier: Identifier;
Service: Shape;
key: string;
stack: string | undefined;
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.type Context.Key = /*unresolved*/ anyKey<function (type parameter) I in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>I, function (type parameter) S in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>S>,
effect: Effect<Types.NoInfer<S>, 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<import TypesTypes.type NoInfer<A> = [A][A extends any
? 0
: never]
Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) S in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>S>, function (type parameter) E in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>E, function (type parameter) R in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, 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<function (type parameter) I in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>I, function (type parameter) E in <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, 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 <I, S, E, R>(service: Context.Key<I, S>, effect: Effect<Types.NoInfer<S>, E, R>): Layer<I, E, Exclude<R, Scope.Scope>>R, import ScopeScope.Scope>>
} = function() {
if (function (local var) arguments: IArgumentsarguments.IArguments.length: numberlength === 1) {
return (effect: anyeffect: any) => const effectImpl: <I, S, E, R>(
service: Context.Key<I, S>,
effect: Effect<S, E, R>
) => Layer<I, E, Exclude<R, Scope.Scope>>
function (local var) arguments: IArgumentsarguments[0], effect: anyeffect)
}
return const effectImpl: <I, S, E, R>(
service: Context.Key<I, S>,
effect: Effect<S, E, R>
) => Layer<I, E, Exclude<R, Scope.Scope>>
function (local var) arguments: IArgumentsarguments[0], function (local var) arguments: IArgumentsarguments[1])
} as any