PHP OOP - issue with Static functions and variable or use Singleton?

Question

I'm creating Class for Tax purpose, which I need to use it on some pages in my app. I need a general suggestion is it a good way or to use Singleton, I don't want to use Singleton but a Static version of my class, here's the code:

class CalculationCommon extends ObjectModel
{

// Customer Address Array Object
public static $userCountryCode;

public static $cartProducts;

public static $shopID;

public static $theTaxRateIs;

public static $context;

public function __construct( $cartProductList  )
{

    self::$shopID           = Context::getContext()->shop->id
    self::$userCountryCode  = cart::getCustomerAddressDetail($cartProductList[0]['id_address_delivery']);
    self::$cartProducts     = $cartProductList;
}

/* 
* @param array Product obj (all products in current cart)
* Calculate the Tax Rate Globally for the cart, instead of caluculating individually everywehre.
* If Address is in Canada then check if the tax rate is Flat or Destination base
* If Outside of Canada then check the export rate whether flat or Individual attribute base
*/

public static function calculateGlobalTaxRate( )
{

    //Check if any attribute is taxable then apply Tax in Cart
    if( self::taxableCart())
    {
        if(self::$userCountryCode[0]['iso_code'] =='CA') // Inside of Canada
        {
            echo "CANADA<br>";
        }
        else
        {
            // Reserved for Export Rate Outside of Canada
        }
    }
    else
        $globalTaxRateIs = 0; // if No attribute prone for tax then no Tax

    // self::$theTaxRateIs = $globalTaxRateIs;

    return $globalTaxRateIs;
}


/*
* Check if any attribute is taxable before apply Tax in Cart
*/
public static function taxableCart()
{

    return true;
}

}

Here's what I'm creating an instance of this class in an abc page.

$this->thisOrderProduct //having an array for current cart products.
$calculationClass = new CalculationCommon( $this->thisOrderProduct );
echo $calculationClass::calculateGlobalTaxRate( );

I'm getting error while accessing the function of this class in another class, Please suggest me what is the best practice or Rules of Thumbs?

Thanks in Advance, Nadeem

Answer 1

$this->thisOrderProduct //having an array for current cart products.
$calculationClass = new CalculationCommon( $this->thisOrderProduct );
echo $calculationClass::calculateGlobalTaxRate( );

You should really study a little bit more about PHP syntax.

If you are using static , there is no need for instantiation, but the way you are trying to do doesn't work.

You don't need static neither singleton at all, just write a regular class. Also, your properties should never be public.