add an item to an array IF conditional statement

Question

I have a protected array.

class Tric_FullCircle_Model_Product_Adapter extends OnePica_FullCircle_Model_Product_Adapter
{
    /**
     * Global company number
     */
    protected $_globalCompanyNumber = null;

    /**
     * Tax Classes
     */
    protected $_taxClasses = null;

    /**
     * Attributes to update
     *
     * @var array
     */    

    protected $_attributesToUpdate = array( 
        'name', 
        'description', 
        'price', 
        'tax_class_id', 
        'weight', 
        'country_of_manufacture', 
        'specifications', 
        'tric_cn', 
        'tric_style', 
        'tric_color', 
        'tric_div', 
        'tric_div_desc', 
    );

I want to add 'special_price' if it matches a particular default store which 1.

I keep throwing syntax errors in my protected variable array. Do i use an array_diff? or just append it like this $arr[] = 'special_price';

I tried something like this

if (Mage::app()->getStore()->getStoreId() !== Mage::app()->getWebsites()[1]->getDefaultStore()->getStoreId()) {
    $arr[] = 'special_price';
}

and this

if (Mage::app()->getStore()->getStoreId() === Mage::app()->getWebsites()[1]->getDefaultStore()->getStoreId()) {
    $_attributesToUpdate = array_diff(fieldNames, array('special_price'));
}

Answer 1

Access your protected array with $this->

Change

arr[] = 'special_price';

To

$this->arr[] = 'special_price';

OR

Change

_attributesToUpdate = array_diff(fieldNames, array('special_price'));

To

$this->_attributesToUpdate = array_diff(fieldNames, array('special_price'));