How do I override a function from a module?

Question

Firstly, sorry if this answer is covered elsewhere. I've done a lot of searching and can only find info on overring theme functions and hooks.

I am using a module that builds a price table for Drupal Commerce items. There is a function that formats the table headers:

/**
 * Helper function that takes care of the quantity displayed in the headers of 
 * the price table.
 */
function commerce_price_table_display_quantity_headers($item) {
  // Set the quantity text to unlimited if it's -1.
  $max_qty = $item['max_qty'] == -1 ? t('Unlimited') : $item['max_qty'];
  // If max and min qtys are the same, only show one.
  if ($item['min_qty'] == $max_qty) {
    $quantity_text = $item['min_qty'];
  }
  else {
    $quantity_text = $item['min_qty'] . ' - ' . $max_qty;
  }
  return $quantity_text;
}

As you can see, this is not a theme function where I can override it in template.php but I can to tweak some of the output.

Obviously I don't want to edit the module itself in case it gets updated in the future, so, how can I redefine this function so I can chop and change a few things?

My work so far...

So far, I have tried to create it as a seperate module with a few subtle changes to show if it's working or not, but it's not overriding any of the output.

Info file

; $id$
name = Price Table: Tweaked Display
description = A different layout for the price table as shown on the product display nodes
package = Commerce (contrib)
core = 7.x

dependencies[] = commerce_product
dependencies[] = commerce_price
dependencies[] = commerce_price_table

Module File

 /**
 * Override of the helper function that takes care of the quantity displayed in the headers of 
 * the price table.
 */
function commerce_table_tweak_display_quantity_headers($item) {
  // Set the quantity text to unlimited if it's -1.
  $max_qty = $item['max_qty'] == -1 ? t('Unlimited gnhh') : $item['max_qty'];
  // If max and min qtys are the same, only show one.
  if ($item['min_qty'] == $max_qty) {
    $quantity_text = $item['min_qty'];
  }
  else {
    $quantity_text = $item['min_qty'] . ' - this is working - ' . $max_qty;
  }
  return $quantity_text;
}

Answer 1

It's Drupal...there's always a way, but the amount of time it will take to do might make you think twice :)

If you look a bit further up the food chain so-to-speak you'll see that this function is exclusively used by commerce_price_table_field_formatter_view(), which declares a field formatter that is used for the commerce_price_table field type.

With that in mind, you can quite easily implement your own field formatter, assign it to the commerce_price_table field type, and use as much custom code as you want, all the time keeping in line with best practices.

Basically you need to implement hook_field_formatter_info():

function MYMODULE_field_formatter_info() {
  return array(
    'MYMODULE_commerce_multiprice_default' => array(
      'label' => t('MyModule Price chart'),
      'field types' => array('commerce_price_table'),
      'settings' => array(
        'calculation' => FALSE,
        'price_label' => t('Price'),
        'quantity_label' => t('Quantity'),
        'table_orientation' => t('Orientation'),
      ),
    ),
  );
}

And then implement hook_field_formatter_view(), field_formatter_settings_form() and (optionally) hook_field_formatter_summary().

For each of these functions just take the code from the same function in the contrib module, and make the changes where you need to.

Answer 2

Seems, you can’t override this function because it doesn’t use theme or hook workflow.

The only way - is to directly change commerce_price_table_display_quantity_headers() function. Then create a patch with you changes.

Later if you update the Commerce module - you will need apply your patch.

Answer 3

I think Eugene’s answer is correct that you can't do it without overwriting directly.

However, what I have found useful is that if it’s absolutely necessary to do this, move this module from your sites/all/modules/contrib directory to sites/all/modules/custom dir so that you can be aware of and keep track of the fact that you made custom changes.