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peek.ts
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peek.ts
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import type { IteratorReturnValue, UniversalIterable } from '@/types'
import { IterableTypeException, isAsyncIterable, isIterable } from '@/utils'
import { tap } from '../strict/tap'
import { map } from './map'
/**
* Call `fn` for each item in the iterable/asyncIterable and return the original iterable/asyncIterable.
*
* @example
* ```typescript
* const iterator = peek(console.log, [1, 2, 3])
*
* for (const v of iterator) {
* // log 1, 2, 3
* // v = 1, 2, 3
* }
*
* const iterator2 = peek(
* (v) => {
* v.a = 'b'
* },
* [{ a: 'a' }]
* )
*
* for (const v of iterator) {
* console.log(v) // log {a: 'b'}
* }
* ```
*
* {@link https://github.com/niuiic/fx-flow/blob/main/packages/test/src/pipe/lazy/peek.spec.ts | More examples}
*/
function peek<A>(fn: (args: A) => unknown, iterable: Iterable<A>): IterableIterator<A>
function peek<A>(fn: (args: A) => unknown, iterable: AsyncIterable<A>): AsyncIterableIterator<A>
function peek<A>(
fn: (args: A) => unknown
): (iterable: UniversalIterable<A>) => IteratorReturnValue<UniversalIterable<A>>
function peek<A>(
fn: (args: A) => unknown,
iterable?: UniversalIterable<A>
):
| IteratorReturnValue<UniversalIterable<A>>
| ((iterable: UniversalIterable<A>) => IteratorReturnValue<UniversalIterable<A>>) {
type ReturnValue = IteratorReturnValue<UniversalIterable<A>>
if (iterable === undefined) {
return (iterable: UniversalIterable<A>) => peek(fn, iterable as any) as ReturnValue
}
if (isIterable(iterable)) {
return map(tap(fn as any), iterable) as ReturnValue
}
if (isAsyncIterable(iterable)) {
return map(tap(fn as any), iterable) as ReturnValue
}
throw new IterableTypeException()
}
export { peek }