/**
 * Copyright 2013-2014, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule onlyChild
 */
"use strict";

var ReactElement = require('ReactElement');

var invariant = require('invariant');

/**
 * Returns the first child in a collection of children and verifies that there
 * is only one child in the collection. The current implementation of this
 * function assumes that a single child gets passed without a wrapper, but the
 * purpose of this helper function is to abstract away the particular structure
 * of children.
 *
 * @param {?object} children Child collection structure.
 * @return {ReactComponent} The first and only `ReactComponent` contained in the
 * structure.
 */
function onlyChild(children) {
  invariant(
    ReactElement.isValidElement(children),
    'onlyChild must be passed a children with exactly one child.'
  );
  return children;
}

module.exports = onlyChild;
