<K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (
self: ReadonlyRecord<K, A>
) => Option.Option<Record<K, A | B>>
<K extends string | symbol, A, B>(
self: ReadonlyRecord<K, A>,
key: NoInfer<K>,
f: (a: A) => B
): Option.Option<Record<K, A | B>>Applies a function to the element at the specified key safely, creating a new record,
or return Option.none() if the key doesn't exist.
Example (Modifying a value at a key)
import { Record } from "effect"
const f = (x: number) => x * 2
const input: Record<string, number> = { a: 3 }
Record.modify(input, "a", f) // Option.some({ a: 6 })
Record.modify(input, "b", f) // Option.none()export const const modify: {
<K extends string | symbol, A, B>(
key: NoInfer<K>,
f: (a: A) => B
): (
self: ReadonlyRecord<K, A>
) => Option.Option<Record<K, A | B>>
<K extends string | symbol, A, B>(
self: ReadonlyRecord<K, A>,
key: NoInfer<K>,
f: (a: A) => B
): Option.Option<Record<K, A | B>>
}
Applies a function to the element at the specified key safely, creating a new record,
or return Option.none() if the key doesn't exist.
Example (Modifying a value at a key)
import { Record } from "effect"
const f = (x: number) => x * 2
const input: Record<string, number> = { a: 3 }
Record.modify(input, "a", f) // Option.some({ a: 6 })
Record.modify(input, "b", f) // Option.none()
modify: {
<function (type parameter) K in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>K extends string | symbol, function (type parameter) A in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>A, function (type parameter) B in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>B>(
key: NoInfer<K>key: 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) K in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>K>,
f: (a: A) => Bf: (a: Aa: function (type parameter) A in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>A) => function (type parameter) B in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>B
): (self: ReadonlyRecord<K, A>self: type ReadonlyRecord<in out K extends string | symbol, out A> = { readonly [P in K]: A; }Represents a readonly record with keys of type K and values of type A.
This is the foundational type for immutable key-value mappings in Effect.
Example (Defining a readonly record type)
import type { Record } from "effect"
// Creating a readonly record type
type UserRecord = Record.ReadonlyRecord<"name" | "age", string | number>
const user: UserRecord = {
name: "John",
age: 30
}
Namespace containing utility types for working with readonly records.
These types help with type-level operations on record keys and values.
Example (Using readonly record helper types)
import type { Record } from "effect"
// Using NonLiteralKey to convert literal keys to generic types
type GenericKey = Record.ReadonlyRecord.NonLiteralKey<"foo" | "bar"> // string
// Using IntersectKeys to find common keys between record types
type CommonKeys = Record.ReadonlyRecord.IntersectKeys<"a" | "b", "b" | "c"> // "b"
ReadonlyRecord<function (type parameter) K in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>K, function (type parameter) A in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>A>) => import OptionOption.type Option<A> = Option.None<A> | Option.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<type Record<K extends keyof any, T> = {
[P in K]: T
}
Construct a type with a set of properties K of type T
Record<function (type parameter) K in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>K, function (type parameter) A in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>A | function (type parameter) B in <K extends string | symbol, A, B>(key: NoInfer<K>, f: (a: A) => B): (self: ReadonlyRecord<K, A>) => Option.Option<Record<K, A | B>>B>>
<function (type parameter) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K extends string | symbol, function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A, function (type parameter) B in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>B>(
self: ReadonlyRecord<K, A>self: type ReadonlyRecord<in out K extends string | symbol, out A> = { readonly [P in K]: A; }Represents a readonly record with keys of type K and values of type A.
This is the foundational type for immutable key-value mappings in Effect.
Example (Defining a readonly record type)
import type { Record } from "effect"
// Creating a readonly record type
type UserRecord = Record.ReadonlyRecord<"name" | "age", string | number>
const user: UserRecord = {
name: "John",
age: 30
}
Namespace containing utility types for working with readonly records.
These types help with type-level operations on record keys and values.
Example (Using readonly record helper types)
import type { Record } from "effect"
// Using NonLiteralKey to convert literal keys to generic types
type GenericKey = Record.ReadonlyRecord.NonLiteralKey<"foo" | "bar"> // string
// Using IntersectKeys to find common keys between record types
type CommonKeys = Record.ReadonlyRecord.IntersectKeys<"a" | "b", "b" | "c"> // "b"
ReadonlyRecord<function (type parameter) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K, function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A>,
key: NoInfer<K>key: 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) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K>,
f: (a: A) => Bf: (a: Aa: function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A) => function (type parameter) B in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>B
): import OptionOption.type Option<A> = Option.None<A> | Option.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<type Record<K extends keyof any, T> = {
[P in K]: T
}
Construct a type with a set of properties K of type T
Record<function (type parameter) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K, function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A | function (type parameter) B in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>B>>
} = dual<(...args: Array<any>) => any, <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B) => Option.Option<Record<K, A | B>>>(arity: 3, body: <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B) => Option.Option<Record<K, A | B>>): ((...args: Array<any>) => any) & (<K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B) => Option.Option<Record<K, A | B>>) (+1 overload)Creates a function that can be called in data-first style or data-last
(pipe-friendly) style.
When to use
Use to expose one implementation through both direct and pipe-friendly
call styles.
Details
Pass either the arity of the uncurried function or a predicate that decides
whether the current call is data-first. Arity is the common case. Use a
predicate when optional arguments make arity ambiguous.
Example (Selecting data-first or data-last style by arity)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(2, (self, that) => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Defining overloads with call signatures)
import { Function, pipe } from "effect"
const sum: {
(that: number): (self: number) => number
(self: number, that: number): number
} = Function.dual(2, (self: number, that: number): number => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Selecting data-first or data-last style with a predicate)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(
(args) => args.length === 2,
(self, that) => self + that
)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
dual(
3,
<function (type parameter) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K extends string | symbol, function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A, function (type parameter) B in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>B>(
self: ReadonlyRecord<K, A>self: type ReadonlyRecord<in out K extends string | symbol, out A> = { readonly [P in K]: A; }Represents a readonly record with keys of type K and values of type A.
This is the foundational type for immutable key-value mappings in Effect.
Example (Defining a readonly record type)
import type { Record } from "effect"
// Creating a readonly record type
type UserRecord = Record.ReadonlyRecord<"name" | "age", string | number>
const user: UserRecord = {
name: "John",
age: 30
}
Namespace containing utility types for working with readonly records.
These types help with type-level operations on record keys and values.
Example (Using readonly record helper types)
import type { Record } from "effect"
// Using NonLiteralKey to convert literal keys to generic types
type GenericKey = Record.ReadonlyRecord.NonLiteralKey<"foo" | "bar"> // string
// Using IntersectKeys to find common keys between record types
type CommonKeys = Record.ReadonlyRecord.IntersectKeys<"a" | "b", "b" | "c"> // "b"
ReadonlyRecord<function (type parameter) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K, function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A>,
key: NoInfer<K>key: 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) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K>,
f: (a: A) => Bf: (a: Aa: function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A) => function (type parameter) B in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>B
): import OptionOption.type Option<A> = Option.None<A> | Option.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<type Record<K extends keyof any, T> = {
[P in K]: T
}
Construct a type with a set of properties K of type T
Record<function (type parameter) K in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>K, function (type parameter) A in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>A | function (type parameter) B in <K extends string | symbol, A, B>(self: ReadonlyRecord<K, A>, key: NoInfer<K>, f: (a: A) => B): Option.Option<Record<K, A | B>>B>> => {
if (!const has: {
<K extends string | symbol>(key: NoInfer<K>): <
A
>(
self: ReadonlyRecord<K, A>
) => boolean
<K extends string | symbol, A>(
self: ReadonlyRecord<K, A>,
key: NoInfer<K>
): boolean
}
self: ReadonlyRecord<K, A>self, key: NoInfer<K>key)) return import OptionOption.const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none()
return import OptionOption.const some: <A>(value: A) => Option<A>Wraps the given value into an Option to represent its presence.
When to use
Use to wrap a known present value as Option
- Returning a successful result from a partial function
Details
- Always returns
Some<A>
- Does not filter
null or undefined; use
fromNullishOr
for that
Example (Wrapping a value)
import { Option } from "effect"
// ┌─── Option<number>
// ▼
const value = Option.some(1)
console.log(value)
// Output: { _id: 'Option', _tag: 'Some', value: 1 }
some({ ...self: ReadonlyRecord<K, A>self, [key: NoInfer<K>key]: f: (a: A) => Bf(self: ReadonlyRecord<K, A>self[key: NoInfer<K>key]) })
}
)