/**
 * Copyright 2013 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @providesModule emptyFunction
 */

var copyProperties = require('copyProperties');

function makeEmptyFunction(arg) {
  return function() {
    return arg;
  };
}

/**
 * This function accepts and discards inputs; it has no side effects. This is
 * primarily useful idiomatically for overridable function endpoints which
 * always need to be callable, since JS lacks a null-call idiom ala Cocoa.
 */
function emptyFunction() {}

copyProperties(emptyFunction, {
  thatReturns: makeEmptyFunction,
  thatReturnsFalse: makeEmptyFunction(false),
  thatReturnsTrue: makeEmptyFunction(true),
  thatReturnsNull: makeEmptyFunction(null),
  thatReturnsThis: function() { return this; },
  thatReturnsArgument: function(arg) { return arg; },
  mustImplement: function(module, property) {
    return function() {
      if (__DEV__) {
        throw new Error(module + '.' + property + ' must be implemented!');
      }
    };
  }
});

module.exports = emptyFunction;
