Merge pull request #179 from webdeveric/fix/range

fix(range): use function overloading for better return type

Author: webdeveric

src/predicate/factory/range.ts

@@ -1,6 +1,10 @@
 import type { TypePredicateFn } from '../../types/functions.js';
 
-export const range = <Type extends number | bigint>(min: Type, max: Type): TypePredicateFn<Type> => {
+export function range(min: number, max: number): TypePredicateFn<number>;
+
+export function range(min: bigint, max: bigint): TypePredicateFn<bigint>;
+
+export function range(min: number | bigint, max: number | bigint): TypePredicateFn<number | bigint> {
   if (min === Number.NEGATIVE_INFINITY && max === Number.POSITIVE_INFINITY) {
     throw new RangeError('min and max cannot be -Infinity and Infinity');
   }
@@ -13,6 +17,6 @@ export const range = <Type extends number | bigint>(min: Type, max: Type): TypeP
     throw new RangeError('min must be less than max');
   }
 
-  return (input: unknown): input is Type =>
+  return (input: unknown): input is number | bigint =>
     (typeof input === 'number' || typeof input === 'bigint') && input >= min && input <= max;
-};
+}

test/predicate/factory/range.test-d.ts

@@ -0,0 +1,12 @@
+import { describe, expectTypeOf, it } from 'vitest';
+
+import { range } from '../../../src/predicate/factory/range.js';
+
+import type { TypePredicateFn } from '../../../src/types/functions.js';
+
+describe('range()', () => {
+  it('Returns a type predicate function', () => {
+    expectTypeOf(range(1, 100)).toEqualTypeOf<TypePredicateFn<number>>();
+    expectTypeOf(range(1n, 100n)).toEqualTypeOf<TypePredicateFn<bigint>>();
+  });
+});