feat: add FlattenArrayType utility type (#110)

halvaradop · Sep 11, 2024 · 85df552 · 85df552
1 parent dfab5cc
commit 85df552
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diff --git a/src/array-types.ts b/src/array-types.ts
@@ -259,3 +259,15 @@ type ZipImplementation<T, U, Build extends unknown[] = []> = T extends [infer It
  * type Zip2 = Zip<[1, 2, 3], ["a", "b"]>;
  */
 export type Zip<Array1 extends unknown[], Array2 extends unknown[]> = ZipImplementation<Array1, Array2>;
+
+/**
+ * Returns the flatten type of an array.
+ *
+ * @example
+ * // Expected: number
+ * type Flatten1 = FlattenArrayType<number[][]>;
+ *
+ * // Expected: string
+ * type Flatten2 = FlattenArrayType<string[][][]>;
+ */
+export type FlattenArrayType<Array> = Array extends (infer Type)[] ? FlattenArrayType<Type> : Array;
diff --git a/test/array-types.test.ts b/test/array-types.test.ts
@@ -136,3 +136,13 @@ describe("Zip", () => {
 		>();
 	});
 });
+
+describe("FlattenArrayType", () => {
+	test("Flatten an array type", () => {
+		expectTypeOf<utilities.FlattenArrayType<number[]>>().toEqualTypeOf<number>();
+		expectTypeOf<utilities.FlattenArrayType<number[][]>>().toEqualTypeOf<number>();
+		expectTypeOf<utilities.FlattenArrayType<number[][][]>>().toEqualTypeOf<number>();
+		expectTypeOf<utilities.FlattenArrayType<string[][][][]>>().toEqualTypeOf<string>();
+		expectTypeOf<utilities.FlattenArrayType<unknown[][][][]>>().toEqualTypeOf<unknown>();
+	});
+});