<S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(
f: (a: ReadonlyArray.Infer<S>, i: number) => T
): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>
<A, B>(
self: NonEmptyReadonlyArray<A>,
f: (a: A, i: number) => NonEmptyReadonlyArray<B>
): NonEmptyArray<B>
<A, B>(
self: ReadonlyArray<A>,
f: (a: A, i: number) => ReadonlyArray<B>
): Array<B>Maps each element to an array and flattens the results into a single array.
When to use
Use to map each array element to zero or more values and concatenate the results in one pass.
Details
The function receives (element, index). This returns NonEmptyArray when
both the input and mapped arrays are non-empty.
Example (Flat mapping an array)
import { Array } from "effect"
console.log(Array.flatMap([1, 2, 3], (x) => [x, x * 2])) // [1, 2, 2, 4, 3, 6]Source effect/Array.ts:352722 lines
export const const flatMap: {
<
S extends ReadonlyArray<any>,
T extends ReadonlyArray<any>
>(
f: (a: ReadonlyArray.Infer<S>, i: number) => T
): (
self: S
) => ReadonlyArray.AndNonEmpty<
S,
T,
ReadonlyArray.Infer<T>
>
<A, B>(
self: NonEmptyReadonlyArray<A>,
f: (
a: A,
i: number
) => NonEmptyReadonlyArray<B>
): NonEmptyArray<B>
<A, B>(
self: ReadonlyArray<A>,
f: (a: A, i: number) => ReadonlyArray<B>
): Array<B>
}
Maps each element to an array and flattens the results into a single array.
When to use
Use to map each array element to zero or more values and concatenate the
results in one pass.
Details
The function receives (element, index). This returns NonEmptyArray when
both the input and mapped arrays are non-empty.
Example (Flat mapping an array)
import { Array } from "effect"
console.log(Array.flatMap([1, 2, 3], (x) => [x, x * 2])) // [1, 2, 2, 4, 3, 6]
flatMap: {
<function (type parameter) S in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>S extends interface ReadonlyArray<T>ReadonlyArray<any>, function (type parameter) T in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>T extends interface ReadonlyArray<T>ReadonlyArray<any>>(
f: (
a: ReadonlyArray.Infer<S>,
i: number
) => T
a: ReadonlyArray.Infer<S>a: ReadonlyArray.type ReadonlyArray.Infer<S extends Iterable<any>> = S extends readonly (infer A)[] ? A : S extends Iterable<infer A> ? A : neverInfers the element type of an iterable.
Example (Inferring an element type)
import type { Array } from "effect"
type StringArrayType = Array.ReadonlyArray.Infer<ReadonlyArray<string>>
// StringArrayType is string
Infer<function (type parameter) S in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>S>, i: numberi: number) => function (type parameter) T in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>T
): (self: S extends ReadonlyArray<any>self: function (type parameter) S in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>S) => ReadonlyArray.type ReadonlyArray.AndNonEmpty<S extends Iterable<any>, T extends Iterable<any>, A> = S extends readonly [any, ...any[]] ? T extends readonly [any, ...any[]] ? [A, ...A[]] : A[] : A[]Creates a non-empty array only if both inputs are non-empty.
Example (Preserving non-emptiness from both inputs)
import type { Array } from "effect"
type Result = Array.ReadonlyArray.AndNonEmpty<
readonly [number],
readonly [string],
boolean
>
// Result is NonEmptyArray<boolean>
AndNonEmpty<function (type parameter) S in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>S, function (type parameter) T in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>T, ReadonlyArray.type ReadonlyArray.Infer<S extends Iterable<any>> = S extends readonly (infer A)[] ? A : S extends Iterable<infer A> ? A : neverInfers the element type of an iterable.
Example (Inferring an element type)
import type { Array } from "effect"
type StringArrayType = Array.ReadonlyArray.Infer<ReadonlyArray<string>>
// StringArrayType is string
Infer<function (type parameter) T in <S extends ReadonlyArray<any>, T extends ReadonlyArray<any>>(f: (a: ReadonlyArray.Infer<S>, i: number) => T): (self: S) => ReadonlyArray.AndNonEmpty<S, T, ReadonlyArray.Infer<T>>T>>
<function (type parameter) A in <A, B>(self: NonEmptyReadonlyArray<A>, f: (a: A, i: number) => NonEmptyReadonlyArray<B>): NonEmptyArray<B>A, function (type parameter) B in <A, B>(self: NonEmptyReadonlyArray<A>, f: (a: A, i: number) => NonEmptyReadonlyArray<B>): NonEmptyArray<B>B>(self: NonEmptyReadonlyArray<A>(parameter) self: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
slice: (start?: number, end?: number) => Array<A>;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): this is readonly S[]; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: ReadonlyArray<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: ReadonlyArray<A>) => A, initialValue: A): A; (callbac…;
find: { (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: ReadonlyArray<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: ReadonlyArray<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
type NonEmptyReadonlyArray<A> = readonly [
A,
...A[]
]
A readonly array guaranteed to have at least one element.
When to use
Use when non-emptiness must be tracked at the type level while preventing mutation.
Many Array module functions accept or return this type.
Example (Typing a non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyReadonlyArray<number> = [1, 2, 3]
const head: number = nonEmpty[0] // guaranteed to exist
NonEmptyReadonlyArray<function (type parameter) A in <A, B>(self: NonEmptyReadonlyArray<A>, f: (a: A, i: number) => NonEmptyReadonlyArray<B>): NonEmptyArray<B>A>, f: (
a: A,
i: number
) => NonEmptyReadonlyArray<B>
a: Aa: function (type parameter) A in <A, B>(self: NonEmptyReadonlyArray<A>, f: (a: A, i: number) => NonEmptyReadonlyArray<B>): NonEmptyArray<B>A, i: numberi: number) => type NonEmptyReadonlyArray<A> = readonly [
A,
...A[]
]
A readonly array guaranteed to have at least one element.
When to use
Use when non-emptiness must be tracked at the type level while preventing mutation.
Many Array module functions accept or return this type.
Example (Typing a non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyReadonlyArray<number> = [1, 2, 3]
const head: number = nonEmpty[0] // guaranteed to exist
NonEmptyReadonlyArray<function (type parameter) B in <A, B>(self: NonEmptyReadonlyArray<A>, f: (a: A, i: number) => NonEmptyReadonlyArray<B>): NonEmptyArray<B>B>): type NonEmptyArray<A> = [A, ...A[]]A mutable array guaranteed to have at least one element.
When to use
Use when mutation is acceptable and non-emptiness must be tracked at the type
level.
Details
This is the mutable counterpart of
NonEmptyReadonlyArray
. Most Array
module functions return NonEmptyArray when the result is guaranteed
non-empty.
Example (Typing a mutable non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyArray<number> = [1, 2, 3]
nonEmpty.push(4)
NonEmptyArray<function (type parameter) B in <A, B>(self: NonEmptyReadonlyArray<A>, f: (a: A, i: number) => NonEmptyReadonlyArray<B>): NonEmptyArray<B>B>
<function (type parameter) A in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>A, function (type parameter) B in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>B>(self: readonly A[]self: interface ReadonlyArray<T>ReadonlyArray<function (type parameter) A in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>A>, f: (a: A, i: number) => ReadonlyArray<B>f: (a: Aa: function (type parameter) A in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>A, i: numberi: number) => interface ReadonlyArray<T>ReadonlyArray<function (type parameter) B in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>B>): interface Array<T>Array<function (type parameter) B in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>B>
} = dual<(...args: Array<any>) => any, <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>) => Array<B>>(arity: 2, body: <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>) => Array<B>): ((...args: Array<any>) => any) & (<A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>) => Array<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: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>A, function (type parameter) B in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>B>(self: readonly A[]self: interface ReadonlyArray<T>ReadonlyArray<function (type parameter) A in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>A>, f: (a: A, i: number) => ReadonlyArray<B>f: (a: Aa: function (type parameter) A in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>A, i: numberi: number) => interface ReadonlyArray<T>ReadonlyArray<function (type parameter) B in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>B>): interface Array<T>Array<function (type parameter) B in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>B> => {
if (const isReadonlyArrayEmpty: <A>(
self: readonly A[]
) => self is readonly []
Checks whether a ReadonlyArray is empty, narrowing the type to readonly [].
Example (Checking for an empty readonly array)
import { Array } from "effect"
console.log(Array.isReadonlyArrayEmpty([])) // true
console.log(Array.isReadonlyArrayEmpty([1, 2, 3])) // false
isReadonlyArrayEmpty(self: readonly A[]self)) {
return []
}
const const out: B[]out: interface Array<T>Array<function (type parameter) B in <A, B>(self: ReadonlyArray<A>, f: (a: A, i: number) => ReadonlyArray<B>): Array<B>B> = []
for (let let i: numberi = 0; let i: numberi < self: readonly A[]self.globalThis.ReadonlyArray<T>.length: numberGets the length of the array. This is a number one higher than the highest element defined in an array.
length; let i: numberi++) {
const const inner: readonly B[]inner = f: (a: A, i: number) => ReadonlyArray<B>f(self: readonly A[]self[let i: numberi], let i: numberi)
for (let let j: numberj = 0; let j: numberj < const inner: readonly B[]inner.globalThis.ReadonlyArray<T>.length: numberGets the length of the array. This is a number one higher than the highest element defined in an array.
length; let j: numberj++) {
const out: B[]out.Array<B>.push(...items: B[]): numberAppends new elements to the end of an array, and returns the new length of the array.
push(const inner: readonly B[]inner[let j: numberj])
}
}
return const out: B[]out
}
)Referenced by 4 symbols