var classof = require('../internals/classof');
var getMethod = require('../internals/get-method');
var isNullOrUndefined = require('../internals/is-null-or-undefined');
var Iterators = require('../internals/iterators');
var wellKnownSymbol = require('../internals/well-known-symbol');

var ITERATOR = wellKnownSymbol('iterator');

module.exports = function (it) {
  if (!isNullOrUndefined(it)) return getMethod(it, ITERATOR)
    || getMethod(it, '@@iterator')
    || Iterators[classof(it)];
};