feat(micro-dash): improve typing of reduce() and reduceRight()

Closes #20
simontonsoftware · Jan 7, 2021 · 6c5500d · 6c5500d
1 parent c0aa75e
commit 6c5500d
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Showing 6 changed files with 350 additions and 29 deletions.
diff --git a/projects/micro-dash/src/lib/collection/reduce-right.spec.ts b/projects/micro-dash/src/lib/collection/reduce-right.spec.ts
@@ -5,7 +5,12 @@ import { reduceRight } from './reduce-right';
 describe('reduceRight()', () => {
   it('works with `undefined`', () => {
     expect(reduceRight(undefined, () => 1, 2)).toEqual(2);
-    expect(reduceRight(undefined, () => 1)).toBeUndefined();
+    expect(reduceRight(undefined as any, () => 1)).toBeUndefined();
+  });
+
+  it('works with `null`', () => {
+    expect(reduceRight(null, () => 1, 2)).toEqual(2);
+    expect(reduceRight(null as any, () => 1)).toBeUndefined();
   });
 
   //

diff --git a/projects/micro-dash/src/lib/collection/reduce-right.ts b/projects/micro-dash/src/lib/collection/reduce-right.ts
@@ -1,4 +1,4 @@
-import { ObjectWith } from '../interfaces';
+import { IfCouldBe, Nil } from '../interfaces';
 import { forEachRight } from './for-each-right';
 import { doReduce } from './reduce-utils';
 
@@ -9,22 +9,35 @@ import { doReduce } from './reduce-utils';
  * - Lodash: 14,053 bytes
  * - Micro-dash: 357 bytes
  */
-export function reduceRight<E>(
-  array: E[] | undefined,
-  iteratee: (accumulator: E, value: E, index: number) => E,
-): E;
+
+export function reduceRight<T extends any[] | Nil>(
+  array: T,
+  iteratee: (
+    accumulator: NonNullable<T>[number],
+    value: NonNullable<T>[number],
+    index: number,
+  ) => NonNullable<T>[number],
+): NonNullable<T>[number] | IfCouldBe<T, Nil, undefined>;
 export function reduceRight<E, A>(
-  array: E[] | undefined,
+  array: E[] | Nil,
   iteratee: (accumulator: A, value: E, index: number) => A,
   accumulator: A,
 ): A;
-export function reduceRight<E>(
-  array: ObjectWith<E> | undefined,
-  iteratee: (accumulator: E, value: E, key: keyof E) => E,
-): E;
-export function reduceRight<E, A>(
-  array: ObjectWith<E> | undefined,
-  iteratee: (accumulator: A, value: E, key: keyof E) => A,
+export function reduceRight<T>(
+  object: T,
+  iteratee: (
+    accumulator: NonNullable<T>[keyof NonNullable<T>],
+    value: NonNullable<T>[keyof NonNullable<T>],
+    key: keyof NonNullable<T>,
+  ) => NonNullable<T>[keyof NonNullable<T>],
+): NonNullable<T>[keyof NonNullable<T>] | IfCouldBe<T, Nil, undefined>;
+export function reduceRight<T, A>(
+  object: T,
+  iteratee: (
+    accumulator: A,
+    value: NonNullable<T>[keyof NonNullable<T>],
+    key: keyof NonNullable<T>,
+  ) => A,
   accumulator: A,
 ): A;
 

diff --git a/projects/micro-dash/src/lib/collection/reduce.spec.ts b/projects/micro-dash/src/lib/collection/reduce.spec.ts
@@ -5,7 +5,12 @@ import { reduce } from './reduce';
 describe('reduce()', () => {
   it('works with `undefined`', () => {
     expect(reduce(undefined, () => 1, 2)).toEqual(2);
-    expect(reduce(undefined, () => 1)).toBeUndefined();
+    expect(reduce(undefined as any, () => 1)).toBeUndefined();
+  });
+
+  it('works with `null`', () => {
+    expect(reduce(null, () => 1, 2)).toEqual(2);
+    expect(reduce(null as any, () => 1)).toBeUndefined();
   });
 
   //

diff --git a/projects/micro-dash/src/lib/collection/reduce.ts b/projects/micro-dash/src/lib/collection/reduce.ts
@@ -1,4 +1,4 @@
-import { ObjectWith } from '../interfaces';
+import { IfCouldBe, Nil } from '../interfaces';
 import { forEach } from './for-each';
 import { doReduce } from './reduce-utils';
 
@@ -9,24 +9,38 @@ import { doReduce } from './reduce-utils';
  * - Lodash: 14,074 bytes
  * - Micro-dash: 361 bytes
  */
-export function reduce<E>(
-  array: E[] | undefined,
-  iteratee: (accumulator: E, value: E, index: number) => E,
-): E;
+
+export function reduce<T extends any[] | Nil>(
+  array: T,
+  iteratee: (
+    accumulator: NonNullable<T>[number],
+    value: NonNullable<T>[number],
+    index: number,
+  ) => NonNullable<T>[number],
+): NonNullable<T>[number] | IfCouldBe<T, Nil, undefined>;
 export function reduce<E, A>(
-  array: E[] | undefined,
+  array: E[] | Nil,
   iteratee: (accumulator: A, value: E, index: number) => A,
-  accumulator?: A,
+  accumulator: A,
 ): A;
-export function reduce<E>(
-  array: ObjectWith<E> | undefined,
-  iteratee: (accumulator: E, value: E, key: keyof E) => E,
-): E;
-export function reduce<E, A>(
-  array: ObjectWith<E> | undefined,
-  iteratee: (accumulator: A, value: E, key: keyof E) => A,
+export function reduce<T>(
+  object: T,
+  iteratee: (
+    accumulator: NonNullable<T>[keyof NonNullable<T>],
+    value: NonNullable<T>[keyof NonNullable<T>],
+    key: keyof NonNullable<T>,
+  ) => NonNullable<T>[keyof NonNullable<T>],
+): NonNullable<T>[keyof NonNullable<T>] | IfCouldBe<T, Nil, undefined>;
+export function reduce<T, A>(
+  object: T,
+  iteratee: (
+    accumulator: A,
+    value: NonNullable<T>[keyof NonNullable<T>],
+    key: keyof NonNullable<T>,
+  ) => A,
   accumulator: A,
 ): A;
+
 export function reduce(collection: any, iteratee: any, accumulator?: any): any {
   return doReduce(
     forEach,

diff --git a/projects/micro-dash/src/typing-tests/collection/reduce-right.dts-spec.ts b/projects/micro-dash/src/typing-tests/collection/reduce-right.dts-spec.ts
@@ -0,0 +1,142 @@
+import { reduceRight } from '../../lib/collection';
+import { identity } from '../../lib/util';
+
+type Ary = Array<string | number>;
+type Obj = { a: string; b: number };
+
+declare const a: Ary;
+declare const aOrNull: Ary | null;
+declare const aOrUndefined: Ary | undefined;
+declare const aOrNullOrUndefined: Ary | null | undefined;
+declare const o: Obj;
+declare const oOrNull: Obj | null;
+declare const oOrUndefined: Obj | undefined;
+declare const oOrNullOrUndefined: Obj | null | undefined;
+
+// $ExpectType string | number
+reduceRight(a, identity);
+// $ExpectType string | number | undefined
+reduceRight(aOrNull, identity);
+// $ExpectType string | number | undefined
+reduceRight(aOrUndefined, identity);
+// $ExpectType string | number | undefined
+reduceRight(aOrNullOrUndefined, identity);
+// $ExpectType number
+reduceRight(a, identity, 4);
+// $ExpectType number
+reduceRight(aOrNull, identity, 4);
+// $ExpectType number
+reduceRight(aOrUndefined, identity, 4);
+// $ExpectType number
+reduceRight(aOrNullOrUndefined, identity, 4);
+
+// $ExpectType string | number
+reduceRight(o, identity);
+// $ExpectType string | number | undefined
+reduceRight(oOrNull, identity);
+// $ExpectType string | number | undefined
+reduceRight(oOrUndefined, identity);
+// $ExpectType string | number | undefined
+reduceRight(oOrNullOrUndefined, identity);
+// $ExpectType number
+reduceRight(o, identity, 4);
+// $ExpectType number
+reduceRight(oOrNull, identity, 4);
+// $ExpectType number
+reduceRight(oOrUndefined, identity, 4);
+// $ExpectType number
+reduceRight(oOrNullOrUndefined, identity, 4);
+
+reduceRight(
+  a,
+  (
+    // $ExpectType string | number
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType number
+    index,
+  ) => 1,
+);
+reduceRight(
+  aOrNull,
+  (
+    // $ExpectType string | number
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType number
+    index,
+  ) => 1,
+);
+reduceRight(
+  a,
+  (
+    // $ExpectType Date
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType number
+    index,
+  ) => accumulator,
+  new Date(),
+);
+reduceRight(
+  aOrNull,
+  (
+    // $ExpectType Date
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType number
+    index,
+  ) => accumulator,
+  new Date(),
+);
+
+reduceRight(
+  o,
+  (
+    // $ExpectType string | number
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType "a" | "b"
+    index,
+  ) => 1,
+);
+reduceRight(
+  oOrNull,
+  (
+    // $ExpectType string | number
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType "a" | "b"
+    index,
+  ) => 1,
+);
+reduceRight(
+  o,
+  (
+    // $ExpectType Date
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType "a" | "b"
+    index,
+  ) => accumulator,
+  new Date(),
+);
+reduceRight(
+  oOrNull,
+  (
+    // $ExpectType Date
+    accumulator,
+    // $ExpectType string | number
+    value,
+    // $ExpectType "a" | "b"
+    index,
+  ) => accumulator,
+  new Date(),
+);