Function reconcileChildrenIteratable

packages/react-reconciler/src/ReactChildFiber.js:1310–1374

(
    returnFiber: Fiber,
    currentFirstChild: Fiber | null,
    newChildrenIterable: Iterable<mixed>,
    lanes: Lanes,
  )

  }

  function reconcileChildrenIteratable(
    returnFiber: Fiber,
    currentFirstChild: Fiber | null,
    newChildrenIterable: Iterable<mixed>,
    lanes: Lanes,
  ): Fiber | null {
    // This is the same implementation as reconcileChildrenArray(),
    // but using the iterator instead.

    const iteratorFn = getIteratorFn(newChildrenIterable);

    if (typeof iteratorFn !== 'function') {
      throw new Error(
        'An object is not an iterable. This error is likely caused by a bug in ' +
          'React. Please file an issue.',
      );
    }

    const newChildren = iteratorFn.call(newChildrenIterable);

    if (__DEV__) {
      if (newChildren === newChildrenIterable) {
        // We don't support rendering Generators as props because it's a mutation.
        // See https://github.com/facebook/react/issues/12995
        // We do support generators if they were created by a GeneratorFunction component
        // as its direct child since we can recreate those by rerendering the component
        // as needed.
        const isGeneratorComponent =
          returnFiber.tag === FunctionComponent &&
          // $FlowFixMe[method-unbinding]
          Object.prototype.toString.call(returnFiber.type) ===
            '[object GeneratorFunction]' &&
          // $FlowFixMe[method-unbinding]
          Object.prototype.toString.call(newChildren) === '[object Generator]';
        if (!isGeneratorComponent) {
          if (!didWarnAboutGenerators) {
            console.error(
              'Using Iterators as children is unsupported and will likely yield ' +
                'unexpected results because enumerating a generator mutates it. ' +
                'You may convert it to an array with `Array.from()` or the ' +
                '`[...spread]` operator before rendering. You can also use an ' +
                'Iterable that can iterate multiple times over the same items.',
            );
          }
          didWarnAboutGenerators = true;
        }
      } else if ((newChildrenIterable: any).entries === iteratorFn) {
        // Warn about using Maps as children
        if (!didWarnAboutMaps) {
          console.error(
            'Using Maps as children is not supported. ' +
              'Use an array of keyed ReactElements instead.',
          );
          didWarnAboutMaps = true;
        }
      }
    }