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take.ts
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take.ts
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import type { IteratorReturnValue, UniversalIterable, UniversalIterableItem } from '@/types'
import { IterableTypeException, isAsyncIterable, isIterable } from '@/utils'
function* sync<A>(length: number, iterable: Iterable<A>): IterableIterator<A> {
const iterator = iterable[Symbol.iterator]()
while (length > 0) {
length = length - 1
const cur = iterator.next()
if (cur.done === true) {
break
}
yield cur.value
}
}
function async<A>(length: number, iterable: AsyncIterable<A>): AsyncIterableIterator<A> {
const iterator = iterable[Symbol.asyncIterator]()
return {
[Symbol.asyncIterator]() {
return this
},
async next(concurrent) {
if (length-- < 1) {
return { done: true, value: undefined }
}
return iterator.next(concurrent)
}
}
}
/**
* Returns IterableIterator/AsyncIterableIterator that take `length` values from iterable
*
* @example
* ```typescript
* for (const v of take(2, [1, 2, 3, 4])) {
* console.log(v)
* }
* // 1, 2
* ```
*
* {@link https://github.com/niuiic/fx-flow/blob/main/packages/test/src/pipe/lazy/take.spec.ts | More examples}
*/
function take<A>(length: number, iterable: Iterable<A>): IterableIterator<A>
function take<A>(length: number, iterable: AsyncIterable<A>): AsyncIterableIterator<Awaited<A>>
function take<A extends UniversalIterable>(length: number): (iterable: A) => IteratorReturnValue<A>
function take<A extends UniversalIterable>(
length: number,
iterable?: A
):
| IterableIterator<UniversalIterableItem<A>>
| AsyncIterableIterator<UniversalIterableItem<A>>
| ((iterable: A) => IteratorReturnValue<A>) {
if (length <= 0) {
throw new Error('"length" must be greater than 0')
}
if (iterable === undefined) {
return (iterable: A) => take(length, iterable as any) as IteratorReturnValue<A>
}
if (isIterable<UniversalIterableItem<A>>(iterable)) {
return sync(length, iterable)
}
if (isAsyncIterable<UniversalIterableItem<A>>(iterable)) {
return async(length, iterable)
}
throw new IterableTypeException()
}
export { take }