PHP array of objects requires me to clone each object or it will persist changes

Question

I have a class that has an array of objects. I have a function that loops over the array, and formats a value, and then just puts these formatted values into a separate array... and then returns them.

Here is relevant code:

class MoneyThing {
    public $taxes = array();

    public function formatTaxes(){
        // Pretend the $taxes array is populated as such when called, with a single LeviedTax object
        //  Array
        //  (
        //      [0] => LeviedTax Object
        //      (
        //          [name] => HST
        //          [rate] => 13
        //          [total] => 17.55
        //          [harmonized] => 1
        //      )
        //  )

        echo "<pre>".print_r($this->taxes, true)."</pre>";

        $formattedTaxes = $this->taxes;

        foreach($formattedTaxes as $tax){
            // Make a clone of the object.  PHP object are copied to other vars by reference by default.
            // $tax = clone $tax;

            // Just adds a dollar sign
            $tax->total = money_format($tax->total);
            $formattedTaxes[] = $tax;
        }

        echo "<pre>".print_r($this->taxes, true)."</pre>";

        // Will print the 'total' with a dollar sign. Why???:
        //  Array
        //  (
        //      [0] => LeviedTax Object
        //      (
        //          [name] => HST
        //          [rate] => 13
        //          [total] => $17.55
        //          [harmonized] => 1
        //      )
        //  )

        return $formattedTaxes;
    }
}

I have printed the class's array before and after the foreach loop. I am seeing the array keep these changes, as if I made them directly by reference within the foreach. I am expecting to have the same array before and after the loop as I'm not even working with said array.

It is my understanding that Arrays are copied plain and simple, whereas Objects are copied by reference. However, since I am copying an array of objects I would expect to not have to use clone because it's not by reference... right?

How come I have to uncomment $tax = clone $tax; in order to not actually persist the formatted values?

Possible duplicate of Are objects in array passed by reference? — Script47
– Script47, Commented Jun 7, 2018 at 3:55

zoonman · Accepted Answer · 2018-06-08 04:52:55Z

3

Objects are always passed by reference. Technically speaking array of objects in PHP is array of references to objects.

From design perspective you are trying to solve the wrong problem.

Fairly speaking you don't need this method. The calls like money_format() should be implemented at the moment of tax output, for example when you will interpolate this into HTML or write into CSV.

If you are really need to output this stuff multiple time, for example you have to print the formatted tax value into dozens different file formats, it is worth to introduce little overhead in the form of formattedTotal property on the LeviedTax class. In this case you will have a setter like

class LeviedTax {
  public function setTotal($total) {
    $this->total = $total;
    $this->formattedTotal = money_format($total);
  }
}

edited Jun 8, 2018 at 4:52

answered Jun 7, 2018 at 4:15

zoonman

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1 Comment

Gurnzbot Over a year ago

Agreed, but I can't update it due to reasons. However, your initial answer regarding the topic was helpful and something I was definitely unaware of :)

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