feat(operators/chunk): improve types

When the `chunkSize` value is known at compile-time, the return type of the operator will now reflect that and return a suitable union of tuples instead of an array with a generic length.

For example, `chunk(3)` will now return `Operator<T, [T] | [T, T] | [T, T, T]>` instead of `Operator<T, Array<T>>`.

Closes #13

src/operators/chunk.ts

@@ -40,13 +40,24 @@ import { Operator } from '../core/types'
  * )
  * // => [[1, 2], [3, 4], [5]]
  */
+export function chunk<T> (chunkSize: 1): Operator<T, [T]>
+export function chunk<T> (chunkSize: 2): Operator<T, [T] | [T, T]>
+export function chunk<T> (chunkSize: 3): Operator<T, [T] | [T, T] | [T, T, T]>
+export function chunk<T> (chunkSize: 4): Operator<T, [T] | [T, T] | [T, T, T] | [T, T, T, T]>
+export function chunk<T> (chunkSize: 5): Operator<T, [T] | [T, T] | [T, T, T] | [T, T, T, T] | [T, T, T, T, T]>
+export function chunk<T> (chunkSize: 6): Operator<T, [T] | [T, T] | [T, T, T] | [T, T, T, T] | [T, T, T, T, T] | [T, T, T, T, T, T]>
+export function chunk<T> (chunkSize: 7): Operator<T, [T] | [T, T] | [T, T, T] | [T, T, T, T] | [T, T, T, T, T] | [T, T, T, T, T, T] | [T, T, T, T, T, T, T]>
+export function chunk<T> (chunkSize: 8): Operator<T, [T] | [T, T] | [T, T, T] | [T, T, T, T] | [T, T, T, T, T] | [T, T, T, T, T, T] | [T, T, T, T, T, T, T] | [T, T, T, T, T, T, T, T]>
+export function chunk<T> (chunkSize: 9): Operator<T, [T] | [T, T] | [T, T, T] | [T, T, T, T] | [T, T, T, T, T] | [T, T, T, T, T, T] | [T, T, T, T, T, T, T] | [T, T, T, T, T, T, T, T] | [T, T, T, T, T, T, T, T, T]>
+export function chunk<T> (chunkSize: 10): Operator<T, [T] | [T, T] | [T, T, T] | [T, T, T, T] | [T, T, T, T, T] | [T, T, T, T, T, T] | [T, T, T, T, T, T, T] | [T, T, T, T, T, T, T, T] | [T, T, T, T, T, T, T, T, T] | [T, T, T, T, T, T, T, T, T, T]>
+export function chunk<T> (chunkSize: number): Operator<T, Array<T>>
 export function chunk<T> (chunkSize: number): Operator<T, Array<T>> {
 
   if (!Number.isInteger(chunkSize) || chunkSize < 1) {
     throw new RangeError(`Chunk size must be an integer not less than 1; an attempt was made to define the chunk size as ${chunkSize}.`)
   }
 
-  return function *(iterable: Iterable<T>): IterableIterator<Array<T>> {
+  return function* (iterable: Iterable<T>): IterableIterator<Array<T>> {
     const buffer: Array<T> = []
     let count: number = 0
     for (const item of iterable) {

tests/operators.spec.ts

@@ -101,6 +101,16 @@ describe(`Operators`, () => {
       chai.assert.throws(() => j.chunk(-1), RangeError)
     })
 
+    it(`infers the correct type for chunk size 1`, () => {
+      const result = j.pipe([1, 2, 3], j.chunk(1))
+      type Test = AssertTrue<IsExact<typeof result, IterableIterator<[number]>>>
+    })
+
+    it(`infers the correct type for chunk size 2`, () => {
+      const result = j.pipe([1, 2, 3], j.chunk(2))
+      type Test = AssertTrue<IsExact<typeof result, IterableIterator<[number] | [number, number]>>>
+    })
+
     it(`@example 1`, () => {
       const actual = j.pipe(
         [1, 2, 3, 4],