Homework/Fakogram REACT project/node_modules/fbjs/lib/countDistinct.js.flow

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @providesModule countDistinct
 * @flow
 */

'use strict';

var Set = require('./Set');

var emptyFunction = require('./emptyFunction');

/**
 * Returns the count of distinct elements selected from an array.
 */
function countDistinct<T1, T2>(iter: Iterable<T1>, selector: (item: T1) => T2): number {
  selector = selector || emptyFunction.thatReturnsArgument;

  var set = new Set();
  for (var val of iter) {
    set.add(selector(val));
  }

  return set.size;
}

module.exports = countDistinct;