Support overloaded functions (TypeScript types) (#48)

index.d.ts

@@ -88,11 +88,12 @@ declare const mem: {
 	<
 		ArgumentsType extends unknown[],
 		ReturnType,
-		CacheKeyType
+		CacheKeyType,
+		FunctionToMemoize = (...arguments: ArgumentsType) => ReturnType
 	>(
-		fn: (...arguments: ArgumentsType) => ReturnType,
+		fn: FunctionToMemoize,
 		options?: mem.Options<ArgumentsType, CacheKeyType, ReturnType>
-	): (...arguments: ArgumentsType) => ReturnType;
+	): FunctionToMemoize;
 
 	/**
 	Clear all cached data of a memoized function.

index.test-d.ts

@@ -3,17 +3,27 @@ import mem = require('.');
 
 const fn = (string: string) => true;
 
-expectType<(string: string) => boolean>(mem(fn));
-expectType<(string: string) => boolean>(mem(fn, {maxAge: 1}));
-expectType<(string: string) => boolean>(mem(fn, {cacheKey: (...arguments_) => arguments_}));
-expectType<(string: string) => boolean>(
+expectType<typeof fn>(mem(fn));
+expectType<typeof fn>(mem(fn, {maxAge: 1}));
+expectType<typeof fn>(mem(fn, {cacheKey: (...arguments_) => arguments_}));
+expectType<typeof fn>(
 	mem(
 		fn,
 		{cacheKey: (arguments_) => arguments_,
 		cache: new Map<[string], {data: boolean; maxAge: number}>()})
 );
-expectType<(string: string) => boolean>(
+expectType<typeof fn>(
 	mem(fn, {cache: new Map<[string], {data: boolean; maxAge: number}>()})
 );
 
+/* Overloaded function tests */
+function overloadedFn(parameter: false): false;
+function overloadedFn(parameter: true): true;
+function overloadedFn(parameter: boolean): boolean {
+	return parameter;
+}
+expectType<typeof overloadedFn>(mem(overloadedFn));
+expectType<true>(mem(overloadedFn)(true));
+expectType<false>(mem(overloadedFn)(false));
+
 mem.clear(fn);

package.json

@@ -40,7 +40,7 @@
 		"ava": "^2.4.0",
 		"delay": "^4.1.0",
 		"serialize-javascript": "^2.1.0",
-		"tsd": "^0.10.0",
+		"tsd": "^0.11.0",
 		"xo": "^0.25.3"
 	}
 }