Make strings iterable (#891)

ark120202 · web-flow · commit fddc544d69b5 · 2020-06-09T18:57:17.000+02:00
* Make strings iterable

* Add changelog
diff --git a/src/lualib/Iterator.ts b/src/lualib/Iterator.ts
@@ -16,16 +16,25 @@ function __TS__IteratorIteratorStep<T>(this: Iterator<T>): [true, T] | [] {
     return [true, result.value];
 }
 
+/** @tupleReturn */
+function __TS__IteratorStringStep(this: string, index: number): [number, string] | [] {
+    index += 1;
+    if (index > this.length) return [];
+    return [index, string.sub(this, index, index)];
+}
+
 /** @tupleReturn */
 function __TS__Iterator<T>(
     this: void,
     iterable: Iterable<T> | GeneratorIterator | readonly T[]
-): [(...args: any[]) => [any, T] | [], ...any[]] {
+): [(...args: any[]) => [any, any] | [], ...any[]] {
     if ("____coroutine" in iterable) {
         return [__TS__IteratorGeneratorStep, iterable];
     } else if (iterable[Symbol.iterator]) {
         const iterator = iterable[Symbol.iterator]();
         return [__TS__IteratorIteratorStep, iterator];
+    } else if (typeof iterable === "string") {
+        return [__TS__IteratorStringStep, iterable, 0];
     } else {
         return ipairs(iterable as readonly T[]) as any;
     }
diff --git a/test/unit/loops.spec.ts b/test/unit/loops.spec.ts
@@ -442,6 +442,16 @@ test("forof with array typed as iterable", () => {
     `.expectToMatchJsResult();
 });
 
+test.each(["", "abc", "a\0c"])("forof string (%p)", string => {
+    util.testFunctionTemplate`
+        const results: string[] = [];
+        for (const x of ${string}) {
+            results.push(x);
+        }
+        return results;
+    `.expectToMatchJsResult();
+});
+
 describe("for...of empty destructuring", () => {
     const declareTests = (destructuringPrefix: string) => {
         test("array", () => {
