<A, B>(f: (a: A) => B): (self: A | undefined) => B | undefined
<A, B>(self: A | undefined, f: (a: A) => B): B | undefinedMaps a defined value with f, or returns undefined unchanged.
When to use
Use to apply a pure transformation to an A | undefined value while
preserving undefined as absence.
export const const map: {
<A, B>(f: (a: A) => B): (
self: A | undefined
) => B | undefined
<A, B>(self: A | undefined, f: (a: A) => B):
| B
| undefined
}
Maps a defined value with f, or returns undefined unchanged.
When to use
Use to apply a pure transformation to an A | undefined value while
preserving undefined as absence.
map: {
<function (type parameter) A in <A, B>(f: (a: A) => B): (self: A | undefined) => B | undefinedA, function (type parameter) B in <A, B>(f: (a: A) => B): (self: A | undefined) => B | undefinedB>(f: (a: A) => Bf: (a: Aa: function (type parameter) A in <A, B>(f: (a: A) => B): (self: A | undefined) => B | undefinedA) => function (type parameter) B in <A, B>(f: (a: A) => B): (self: A | undefined) => B | undefinedB): (self: A | undefinedself: function (type parameter) A in <A, B>(f: (a: A) => B): (self: A | undefined) => B | undefinedA | undefined) => function (type parameter) B in <A, B>(f: (a: A) => B): (self: A | undefined) => B | undefinedB | undefined
<function (type parameter) A in <A, B>(self: A | undefined, f: (a: A) => B): B | undefinedA, function (type parameter) B in <A, B>(self: A | undefined, f: (a: A) => B): B | undefinedB>(self: A | undefinedself: function (type parameter) A in <A, B>(self: A | undefined, f: (a: A) => B): B | undefinedA | undefined, f: (a: A) => Bf: (a: Aa: function (type parameter) A in <A, B>(self: A | undefined, f: (a: A) => B): B | undefinedA) => function (type parameter) B in <A, B>(self: A | undefined, f: (a: A) => B): B | undefinedB): function (type parameter) B in <A, B>(self: A | undefined, f: (a: A) => B): B | undefinedB | undefined
} = dual<(...args: Array<any>) => any, (self: any, f: any) => any>(arity: 2, body: (self: any, f: any) => any): ((...args: Array<any>) => any) & ((self: any, f: any) => any) (+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, (self: anyself, f: anyf) => (self: anyself === var undefinedundefined ? var undefinedundefined : f: anyf(self: anyself)))