Fill the array item with dependencies on other items in PHP

Question

I have an array and want to fill the some items depend on previous item's values:

$order = array(
    'items_price' => 200,
    'tax_price' => 18,
    'total_price' => function () { 
        return $order.items_price + $order.tax_price;
    })

How can I do that?

Answer 1

Well, that actually is doable. You cannot reference values in the array from within the array itself; but if you declare variable references for the needed array values, you can pass those references to the closure (function) using use :

$order = array(
  'items_price' => ($ip = 200),
  'tax_price' => ($tp = 18),
  'total_price' => function() use ($ip, $tp) {
     return $ip + $tp;
  }
);
echo $order['total_price']();

That echoes out 218 ..! But the downside is that the passed references / params are static. Try

$order['items_price'] = 100;
echo $order['total_price']();

The result are a disappointing 218 ... Even though items_price actually are changed to 100, the params passed to total_price are the same as when the array were created. They are not magically updated, the array are not a piece of dynamic code, it is a data structure.

It was a very interesting question indeed, but I do not see any practically use. It seems to me you in this case should use classes instead of arrays.

Answer 2

If you have only 1 element you can use:

    $order = array('items_price' => 200, 'tax_price' => 18);
    $order['total_price'] = $order['items_price'] + $order['tax_price'];

Or if you have orders array like this you can use array map

    $orders = array_map(
        function($element)
        {
            $element['total_price'] = $element['items_price'] + $element['tax_price'];

            return $element;
            },
        $orders
    );