types: fix types in useAtom hook

.changeset/perfect-ducks-poke.md

@@ -0,0 +1,5 @@
+---
+'atomsphere': patch
+---
+
+Fix types in `useAtom` hook

src/__tests__/use-atom.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from 'vitest';
+import { describe, expect, expectTypeOf, it } from 'vitest';
 import { renderHook, waitFor } from '@testing-library/react';
 import { atom } from '../atom';
 import { useAtom } from '../use-atom';
@@ -75,4 +75,23 @@ describe('useAtom', () => {
 			expect(result.current).toBe(2);
 		});
 	});
+
+	it('should have proper types', () => {
+		// Arrange.
+		const countAtom = atom(0);
+		const stringCountAtom = atom((get) => String(get(countAtom)));
+
+		const { result: countResult } = renderHook(() => useAtom(countAtom));
+
+		const { result: doubleCountResult } = renderHook(() =>
+			useAtom(stringCountAtom),
+		);
+
+		// Assert.
+		expectTypeOf(countResult.current).toEqualTypeOf<
+			[number, (value: number | ((prev: number) => number)) => void]
+		>();
+
+		expectTypeOf(doubleCountResult.current).toEqualTypeOf<string>();
+	});
 });

src/use-atom.ts

@@ -1,13 +1,13 @@
 import { useSyncExternalStore } from 'react';
 import type { WritableAtom, ReadableAtom } from './atom';
 
-export function useAtom<T>(
-	atom: WritableAtom<T>,
-): [WritableAtom<T>['get'], WritableAtom<T>['set']];
-
-export function useAtom<T>(atom: ReadableAtom<T>): ReadableAtom<T>['get'];
+type Setter<T> = WritableAtom<T>['set'];
 
-export function useAtom<T>(atom: WritableAtom<T> | ReadableAtom<T>) {
+export function useAtom<T>(atom: WritableAtom<T>): [T, Setter<T>];
+export function useAtom<T>(atom: ReadableAtom<T>): T;
+export function useAtom<T>(
+	atom: WritableAtom<T> | ReadableAtom<T>,
+): [T, Setter<T>] | T {
 	const isWriteableAtom = 'set' in atom;
 	const value = useSyncExternalStore(atom.subscribe, atom.get);