<A>(predicate: (a: NoInfer<A>, i: number) => boolean): (
self: Iterable<A>
) => number
<A>(self: Iterable<A>, predicate: (a: A, i: number) => boolean): numberComputes the number of elements in an iterable that satisfy a predicate.
When to use
Use when you need to count how many elements of an iterable satisfy a predicate.
Details
The predicate receives both the element and its index. Empty iterables return
0.
Example (Counting even numbers)
import { Array } from "effect"
const result = Array.countBy([1, 2, 3, 4, 5], (n) => n % 2 === 0)
console.log(result) // 2export const const countBy: {
<A>(
predicate: (
a: NoInfer<A>,
i: number
) => boolean
): (self: Iterable<A>) => number
<A>(
self: Iterable<A>,
predicate: (a: A, i: number) => boolean
): number
}
Computes the number of elements in an iterable that satisfy a predicate.
When to use
Use when you need to count how many elements of an iterable satisfy a
predicate.
Details
The predicate receives both the element and its index. Empty iterables return
0.
Example (Counting even numbers)
import { Array } from "effect"
const result = Array.countBy([1, 2, 3, 4, 5], (n) => n % 2 === 0)
console.log(result) // 2
countBy: {
<function (type parameter) A in <A>(predicate: (a: NoInfer<A>, i: number) => boolean): (self: Iterable<A>) => numberA>(predicate: (a: NoInfer<A>, i: number) => booleanpredicate: (a: NoInfer<A>a: 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) A in <A>(predicate: (a: NoInfer<A>, i: number) => boolean): (self: Iterable<A>) => numberA>, i: numberi: number) => boolean): (self: Iterable<A>self: interface Iterable<T, TReturn = any, TNext = any>Iterable<function (type parameter) A in <A>(predicate: (a: NoInfer<A>, i: number) => boolean): (self: Iterable<A>) => numberA>) => number
<function (type parameter) A in <A>(self: Iterable<A>, predicate: (a: A, i: number) => boolean): numberA>(self: Iterable<A>self: interface Iterable<T, TReturn = any, TNext = any>Iterable<function (type parameter) A in <A>(self: Iterable<A>, predicate: (a: A, i: number) => boolean): numberA>, predicate: (a: A, i: number) => booleanpredicate: (a: Aa: function (type parameter) A in <A>(self: Iterable<A>, predicate: (a: A, i: number) => boolean): numberA, i: numberi: number) => boolean): number
} = dual<(...args: Array<any>) => any, <A>(self: Iterable<A>, f: (a: A, i: number) => boolean) => number>(arity: 2, body: <A>(self: Iterable<A>, f: (a: A, i: number) => boolean) => number): ((...args: Array<any>) => any) & (<A>(self: Iterable<A>, f: (a: A, i: number) => boolean) => number) (+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>(self: Iterable<A>, f: (a: A, i: number) => boolean): numberA>(
self: Iterable<A>self: interface Iterable<T, TReturn = any, TNext = any>Iterable<function (type parameter) A in <A>(self: Iterable<A>, f: (a: A, i: number) => boolean): numberA>,
f: (a: A, i: number) => booleanf: (a: Aa: function (type parameter) A in <A>(self: Iterable<A>, f: (a: A, i: number) => boolean): numberA, i: numberi: number) => boolean
): number => {
let let count: numbercount = 0
const const as: A[]as = const fromIterable: <A>(
collection: Iterable<A>
) => A[]
Converts an Iterable to an Array.
When to use
Use to convert any Iterable (Set, Generator, etc.) into an array.
Details
If the input is already an array, this returns it by reference without
copying. Otherwise, it creates a new array from the iterable. Use copy if
you need a fresh array even when the input is already an array.
Example (Converting a Set to an array)
import { Array } from "effect"
const result = Array.fromIterable(new Set([1, 2, 3]))
console.log(result) // [1, 2, 3]
fromIterable(self: Iterable<A>self)
for (let let i: numberi = 0; let i: numberi < const as: A[]as.Array<T>.length: numberGets or sets the length of the array. This is a number one higher than the highest index in the array.
length; let i: numberi++) {
const const a: Aa = const as: A[]as[let i: numberi]
if (f: (a: A, i: number) => booleanf(const a: Aa, let i: numberi)) {
let count: numbercount++
}
}
return let count: numbercount
}
)