All.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Config\Model\Config\Source\Locale\Currency;

/**
 * @api
 * @since 100.0.2
 */
class All implements \Magento\Framework\Option\ArrayInterface
{
    /**
     * @var array
     */
    protected $_options;

    /**
     * @var \Magento\Framework\Locale\ListsInterface
     */
    protected $_localeLists;

    /**
     * @param \Magento\Framework\Locale\ListsInterface $localeLists
     */
    public function __construct(\Magento\Framework\Locale\ListsInterface $localeLists)
    {
        $this->_localeLists = $localeLists;
    }

    /**
     * @param bool $isMultiselect
     * @return array
     */
    public function toOptionArray($isMultiselect = false)
    {
        if (!$this->_options) {
            $this->_options = $this->_localeLists->getOptionAllCurrencies();
        }
        $options = $this->_options;
        if (!$isMultiselect) {
            array_unshift($options, ['value' => '', 'label' => '']);
        }

        return $options;
    }
}