<RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<
Context.Context<ROut>,
E,
RIn | Scope.Scope
>Builds a layer into a scoped value.
Example (Building a layer into a context)
import { Context, Effect, Layer } from "effect"
class Database extends Context.Service<Database, {
readonly query: (sql: string) => Effect.Effect<string>
}>()("Database") {}
// Build a layer to get its services
const program = Effect.gen(function*() {
const dbLayer = Layer.succeed(Database, {
query: Effect.fn("Database.query")((sql: string) => Effect.succeed("result"))
})
// Build the layer into Context - automatically manages scope and memoization
const context = yield* Layer.build(dbLayer)
// Extract the specific service from the built layer
const database = Context.get(context, Database)
return yield* database.query("SELECT * FROM users")
})destructors
Source effect/Layer.ts:67410 lines
export const const build: <RIn, E, ROut>(
self: Layer<ROut, E, RIn>
) => Effect<
Context.Context<ROut>,
E,
RIn | Scope.Scope
>
Builds a layer into a scoped value.
Example (Building a layer into a context)
import { Context, Effect, Layer } from "effect"
class Database extends Context.Service<Database, {
readonly query: (sql: string) => Effect.Effect<string>
}>()("Database") {}
// Build a layer to get its services
const program = Effect.gen(function*() {
const dbLayer = Layer.succeed(Database, {
query: Effect.fn("Database.query")((sql: string) => Effect.succeed("result"))
})
// Build the layer into Context - automatically manages scope and memoization
const context = yield* Layer.build(dbLayer)
// Extract the specific service from the built layer
const database = Context.get(context, Database)
return yield* database.query("SELECT * FROM users")
})
build = <function (type parameter) RIn in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>RIn, function (type parameter) E in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>E, function (type parameter) ROut in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>ROut>(
self: Layer<ROut, E, RIn>(parameter) self: {
build: (memoMap: MemoMap, scope: Scope.Scope) => Effect<Context.Context<ROut>, E, RIn>;
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) ROut in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>ROut, function (type parameter) E in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>E, function (type parameter) RIn in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>RIn>
): 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<import ContextContext.interface Context<in Services>Immutable collection of service implementations used for dependency
injection in Effect programs.
Details
The type parameter tracks the service identifiers available in the context.
At runtime, services are stored by each key's string key.
Example (Creating a context with multiple services)
import { Context } from "effect"
// Create a context with multiple services
const Logger = Context.Service<{ log: (msg: string) => void }>("Logger")
const Database = Context.Service<{ query: (sql: string) => string }>(
"Database"
)
const context = Context.make(Logger, {
log: (msg: string) => console.log(msg)
})
.pipe(Context.add(Database, { query: (sql) => `Result: ${sql}` }))
Context<function (type parameter) ROut in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>ROut>, function (type parameter) E in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>E, function (type parameter) RIn in <RIn, E, ROut>(self: Layer<ROut, E, RIn>): Effect<Context.Context<ROut>, E, RIn | Scope.Scope>RIn | import ScopeScope.Scope> =>
import corecore.const withFiber: <
A,
E = never,
R = never
>(
evaluate: (
fiber: FiberImpl<unknown, unknown>
) => Effect.Effect<A, E, R>
) => Effect.Effect<A, E, R>
fiber: internalEffect.FiberImpl<
unknown,
unknown
>
(parameter) fiber: {
id: number;
interruptible: boolean;
currentOpCount: number;
currentLoopCount: number;
_stack: Array<Primitive>;
_observers: Array<(exit: Exit.Exit<A, E>) => void>;
_exit: Exit.Exit<A, E> | undefined;
_currentExit: Exit.Exit<A, E> | undefined;
_children: Set<FiberImpl<any, any>> | undefined;
_interruptedCause: Cause.Cause<never> | undefined;
_yielded: Exit.Exit<any, any> | (() => void) | undefined;
context: Context.Context<never>;
currentScheduler: Scheduler.Scheduler;
currentTracerContext: Tracer.Tracer["context"];
currentSpan: Tracer.AnySpan | undefined;
currentLogLevel: LogLevel.LogLevel;
minimumLogLevel: LogLevel.LogLevel;
currentStackFrame: StackFrame | undefined;
runtimeMetrics: Metric.FiberRuntimeMetricsService | undefined;
maxOpsBeforeYield: number;
currentPreventYield: boolean;
_dispatcher: Scheduler.SchedulerDispatcher | undefined;
currentDispatcher: SchedulerDispatcher;
getRef: <X>(ref: Context.Reference<X>) => X;
addObserver: (cb: (exit: Exit.Exit<unknown, unknown>) => void) => () => void;
interruptUnsafe: (fiberId?: number | undefined, annotations?: Context.Context<never> | undefined) => void;
pollUnsafe: () => Exit.Exit<unknown, unknown> | undefined;
evaluate: (effect: core.Primitive) => void;
runLoop: (effect: core.Primitive) => typeof core.Yield | Exit.Exit<unknown, unknown>;
getCont: <S extends core.contA | core.contE>(symbol: S) => (core.Primitive & Record<S, (value: any, fiber: internalEffect.FiberImpl) => core.Primitive>) | undefined;
yieldWith: (value: Exit.Exit<any, any> | (() => void)) => core.Yield;
children: () => Set<Fiber.Fiber<any, any>>;
pipe: () => unknown;
setContext: (context: Context.Context<never>) => void;
currentSpanLocal: Tracer.Span | undefined;
}
const buildWithMemoMap: {
(memoMap: MemoMap, scope: Scope.Scope): <
RIn,
E,
ROut
>(
self: Layer<ROut, E, RIn>
) => Effect<Context.Context<ROut>, E, RIn>
<RIn, E, ROut>(
self: Layer<ROut, E, RIn>,
memoMap: MemoMap,
scope: Scope.Scope
): Effect<Context.Context<ROut>, E, RIn>
}
self: Layer<ROut, E, RIn>(parameter) self: {
build: (memoMap: MemoMap, scope: Scope.Scope) => Effect<Context.Context<ROut>, E, RIn>;
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; <…;
}
class CurrentMemoMapclass CurrentMemoMap {
key: Identifier;
Service: {
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>;
};
forkOrCreate: <Services>(self: Context.Context<Services>) => MemoMap;
of: (this: void, self: MemoMap) => MemoMap;
context: (self: MemoMap) => Context.Context<CurrentMemoMap>;
use: (f: (service: MemoMap) => Effect<A, E, R>) => Effect<A, E, CurrentMemoMap | R>;
useSync: (f: (service: MemoMap) => A) => Effect<A, never, CurrentMemoMap>;
Identifier: Identifier;
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;
}
Context service for the current MemoMap used in layer construction.
When to use
Use when building custom layer operations that need to access the current
memoization map from the fiber context.
Details
This service wraps a MemoMap as a Context.Service, making it available
for dependency injection during layer construction.
CurrentMemoMap.CurrentMemoMap.forkOrCreate<Services>(self: Context.Context<Services>): MemoMapforkOrCreate(fiber: internalEffect.FiberImpl<
unknown,
unknown
>
(parameter) fiber: {
id: number;
interruptible: boolean;
currentOpCount: number;
currentLoopCount: number;
_stack: Array<Primitive>;
_observers: Array<(exit: Exit.Exit<A, E>) => void>;
_exit: Exit.Exit<A, E> | undefined;
_currentExit: Exit.Exit<A, E> | undefined;
_children: Set<FiberImpl<any, any>> | undefined;
_interruptedCause: Cause.Cause<never> | undefined;
_yielded: Exit.Exit<any, any> | (() => void) | undefined;
context: Context.Context<never>;
currentScheduler: Scheduler.Scheduler;
currentTracerContext: Tracer.Tracer["context"];
currentSpan: Tracer.AnySpan | undefined;
currentLogLevel: LogLevel.LogLevel;
minimumLogLevel: LogLevel.LogLevel;
currentStackFrame: StackFrame | undefined;
runtimeMetrics: Metric.FiberRuntimeMetricsService | undefined;
maxOpsBeforeYield: number;
currentPreventYield: boolean;
_dispatcher: Scheduler.SchedulerDispatcher | undefined;
currentDispatcher: SchedulerDispatcher;
getRef: <X>(ref: Context.Reference<X>) => X;
addObserver: (cb: (exit: Exit.Exit<unknown, unknown>) => void) => () => void;
interruptUnsafe: (fiberId?: number | undefined, annotations?: Context.Context<never> | undefined) => void;
pollUnsafe: () => Exit.Exit<unknown, unknown> | undefined;
evaluate: (effect: core.Primitive) => void;
runLoop: (effect: core.Primitive) => typeof core.Yield | Exit.Exit<unknown, unknown>;
getCont: <S extends core.contA | core.contE>(symbol: S) => (core.Primitive & Record<S, (value: any, fiber: internalEffect.FiberImpl) => core.Primitive>) | undefined;
yieldWith: (value: Exit.Exit<any, any> | (() => void)) => core.Yield;
children: () => Set<Fiber.Fiber<any, any>>;
pipe: () => unknown;
setContext: (context: Context.Context<never>) => void;
currentSpanLocal: Tracer.Span | undefined;
}
FiberImpl<unknown, unknown>.context: Context.Context<never>(property) FiberImpl<unknown, unknown>.context: {
mapUnsafe: ReadonlyMap<string, any>;
mutable: boolean;
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.const getUnsafe: {
<S, I>(service: Key<I, S>): <Services>(
self: Context<Services>
) => S
<Services, S, I>(
self: Context<Services>,
services: Key<I, S>
): S
}
fiber: internalEffect.FiberImpl<
unknown,
unknown
>
(parameter) fiber: {
id: number;
interruptible: boolean;
currentOpCount: number;
currentLoopCount: number;
_stack: Array<Primitive>;
_observers: Array<(exit: Exit.Exit<A, E>) => void>;
_exit: Exit.Exit<A, E> | undefined;
_currentExit: Exit.Exit<A, E> | undefined;
_children: Set<FiberImpl<any, any>> | undefined;
_interruptedCause: Cause.Cause<never> | undefined;
_yielded: Exit.Exit<any, any> | (() => void) | undefined;
context: Context.Context<never>;
currentScheduler: Scheduler.Scheduler;
currentTracerContext: Tracer.Tracer["context"];
currentSpan: Tracer.AnySpan | undefined;
currentLogLevel: LogLevel.LogLevel;
minimumLogLevel: LogLevel.LogLevel;
currentStackFrame: StackFrame | undefined;
runtimeMetrics: Metric.FiberRuntimeMetricsService | undefined;
maxOpsBeforeYield: number;
currentPreventYield: boolean;
_dispatcher: Scheduler.SchedulerDispatcher | undefined;
currentDispatcher: SchedulerDispatcher;
getRef: <X>(ref: Context.Reference<X>) => X;
addObserver: (cb: (exit: Exit.Exit<unknown, unknown>) => void) => () => void;
interruptUnsafe: (fiberId?: number | undefined, annotations?: Context.Context<never> | undefined) => void;
pollUnsafe: () => Exit.Exit<unknown, unknown> | undefined;
evaluate: (effect: core.Primitive) => void;
runLoop: (effect: core.Primitive) => typeof core.Yield | Exit.Exit<unknown, unknown>;
getCont: <S extends core.contA | core.contE>(symbol: S) => (core.Primitive & Record<S, (value: any, fiber: internalEffect.FiberImpl) => core.Primitive>) | undefined;
yieldWith: (value: Exit.Exit<any, any> | (() => void)) => core.Yield;
children: () => Set<Fiber.Fiber<any, any>>;
pipe: () => unknown;
setContext: (context: Context.Context<never>) => void;
currentSpanLocal: Tracer.Span | undefined;
}
FiberImpl<unknown, unknown>.context: Context.Context<never>(property) FiberImpl<unknown, unknown>.context: {
mapUnsafe: ReadonlyMap<string, any>;
mutable: boolean;
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 ScopeScope.const Scope: Context.Service<Scope, Scope>const Scope: {
key: string;
Service: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
};
of: (this: void, self: Scope.Scope) => Scope.Scope;
context: (self: Scope.Scope) => Context.Context<Scope.Scope>;
use: (f: (service: Scope.Scope) => Effect<A, E, R>) => Effect<A, E, Scope.Scope | R>;
useSync: (f: (service: Scope.Scope) => A) => Effect<A, never, Scope.Scope>;
Identifier: Identifier;
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;
}
A Scope represents a context where resources can be acquired and
automatically cleaned up when the scope is closed. Scopes can use
either sequential or parallel finalization strategies.
Example (Managing scoped resources)
import { Effect, Exit, Scope } from "effect"
const program = Effect.gen(function*() {
const scope = yield* Scope.make("sequential")
// Scope has a strategy and state
console.log(scope.strategy) // "sequential"
console.log(scope.state._tag) // "Open"
// Close the scope
yield* Scope.close(scope, Exit.void)
console.log(scope.state._tag) // "Closed"
})
Service tag for the active resource lifetime.
When to use
Use to access the active lifetime when registering finalizers or sharing
resources with the surrounding scope.
Example (Accessing the scope service)
import { Effect, Scope } from "effect"
const program = Effect.gen(function*() {
// Access the scope from the context
const scope = yield* Scope.Scope
// Use the scope for resource management
yield* Scope.addFinalizer(scope, Effect.log("Cleanup"))
})
// Provide a scope to the program
const scoped = Effect.scoped(program)
Scope)
)
)Referenced by 3 symbols