fix(readonly): handle readonly arrays

skovy · Oct 29, 2019 · d7b68ac · d7b68ac
1 parent 595d7db
commit d7b68ac
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Showing 2 changed files with 22 additions and 1 deletion.
diff --git a/src/__tests__/array.test.ts b/src/__tests__/array.test.ts
@@ -142,4 +142,22 @@ describe("array", () => {
     const records = array(record, 2);
     expect(records()).toHaveLength(2);
   });
+
+  test("readonly arrays", () => {
+    type Bar = {
+      index: number;
+    };
+
+    type Foo = {
+      readonly bars: ReadonlyArray<Bar>;
+    };
+
+    const barFactory = define<Bar>({ index: sequence });
+
+    const fooFactory = define<Foo>({
+      bars: array(barFactory, 2)
+    });
+
+    expect(fooFactory().bars).toHaveLength(2);
+  });
 });
diff --git a/src/utils.ts b/src/utils.ts
@@ -46,7 +46,10 @@ type Diff<T, U> = T extends U ? never : T;
 // into `{ b: number; }`
 type DiffProperties<T, U> = Pick<T, Diff<Keys<T>, Keys<U>>>;
 
-export type ArrayElement<ArrayType> = ArrayType extends (infer ElementType)[]
+// Given an array, infer the type of it's elements
+export type ArrayElement<ArrayType> = ArrayType extends ReadonlyArray<
+  infer ElementType
+>
   ? ElementType
   : never;