<B>(onNone: LazyArg<B>): <A>(self: Option<A>) => B | A
<A, B>(self: Option<A>, onNone: LazyArg<B>): A | BExtracts the value from a Some, or evaluates a fallback thunk on None.
When to use
Use when providing a default value for an absent Option
- Unwrapping with lazy evaluation of the fallback
Details
Some→ returns the inner valueNone→ callsonNone()and returns its resultonNoneis only called when needed (lazy)
Example (Unwrapping with a fallback)
import { Option } from "effect"
console.log(Option.some(1).pipe(Option.getOrElse(() => 0)))
// Output: 1
console.log(Option.none().pipe(Option.getOrElse(() => 0)))
// Output: 0export const const getOrElse: {
<B>(onNone: LazyArg<B>): <A>(
self: Option<A>
) => B | A
<A, B>(self: Option<A>, onNone: LazyArg<B>):
| A
| B
}
Extracts the value from a Some, or evaluates a fallback thunk on None.
When to use
Use when providing a default value for an absent Option
- Unwrapping with lazy evaluation of the fallback
Details
Some → returns the inner valueNone → calls onNone() and returns its resultonNone is only called when needed (lazy)
Example (Unwrapping with a fallback)
import { Option } from "effect"
console.log(Option.some(1).pipe(Option.getOrElse(() => 0)))
// Output: 1
console.log(Option.none().pipe(Option.getOrElse(() => 0)))
// Output: 0
getOrElse: {
<function (type parameter) B in <B>(onNone: LazyArg<B>): <A>(self: Option<A>) => B | AB>(onNone: LazyArg<B>onNone: type LazyArg<A> = () => AA zero-argument function that produces a value when invoked.
When to use
Use to type a lazy value provider that should not run until called.
Example (Creating a lazy argument)
import { Function } from "effect"
const constNull: Function.LazyArg<null> = Function.constant(null)
LazyArg<function (type parameter) B in <B>(onNone: LazyArg<B>): <A>(self: Option<A>) => B | AB>): <function (type parameter) A in <A>(self: Option<A>): B | AA>(self: Option<A>self: type Option<A> = None<A> | 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<function (type parameter) A in <A>(self: Option<A>): B | AA>) => function (type parameter) B in <B>(onNone: LazyArg<B>): <A>(self: Option<A>) => B | AB | function (type parameter) A in <A>(self: Option<A>): B | AA
<function (type parameter) A in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BA, function (type parameter) B in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BB>(self: Option<A>self: type Option<A> = None<A> | 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<function (type parameter) A in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BA>, onNone: LazyArg<B>onNone: type LazyArg<A> = () => AA zero-argument function that produces a value when invoked.
When to use
Use to type a lazy value provider that should not run until called.
Example (Creating a lazy argument)
import { Function } from "effect"
const constNull: Function.LazyArg<null> = Function.constant(null)
LazyArg<function (type parameter) B in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BB>): function (type parameter) A in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BA | function (type parameter) B in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BB
} = dual<(...args: Array<any>) => any, <A, B>(self: Option<A>, onNone: LazyArg<B>) => A | B>(arity: 2, body: <A, B>(self: Option<A>, onNone: LazyArg<B>) => A | B): ((...args: Array<any>) => any) & (<A, B>(self: Option<A>, onNone: LazyArg<B>) => 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(
2,
<function (type parameter) A in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BA, function (type parameter) B in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BB>(self: Option<A>self: type Option<A> = None<A> | 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<function (type parameter) A in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BA>, onNone: LazyArg<B>onNone: type LazyArg<A> = () => AA zero-argument function that produces a value when invoked.
When to use
Use to type a lazy value provider that should not run until called.
Example (Creating a lazy argument)
import { Function } from "effect"
const constNull: Function.LazyArg<null> = Function.constant(null)
LazyArg<function (type parameter) B in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BB>): function (type parameter) A in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BA | function (type parameter) B in <A, B>(self: Option<A>, onNone: LazyArg<B>): A | BB => const isNone: <A>(
self: Option<A>
) => self is None<A>
Checks whether an Option is None (absent).
When to use
Use when you need to branch on an absent Option before accessing .value.
Details
- Acts as a type guard, narrowing to
None<A>
Example (Checking for None)
import { Option } from "effect"
console.log(Option.isNone(Option.some(1)))
// Output: false
console.log(Option.isNone(Option.none()))
// Output: true
isNone(self: Option<A>self) ? onNone: LazyArg<B>onNone() : self: Option<A>(parameter) self: {
_tag: "Some";
_op: "Some";
value: A;
valueOrUndefined: A;
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;
}
Some<A>.value: Avalue
)