Is This A Correct Example Usage Of current_filter()?

Question

Is this a good example of usage of current_filter()?

<?php
add_filter("_my_filter","common_function");
add_filter("_another_filter","common_function");
function common_function(){
  $currentFilter = current_filter();
  switch ($currentFilter) {
    case '_my_filter':
      echo "Called by My Filter";
      break;
    case '_another_filter':
      echo "Called by another filter";
      break;
  }
}

So I am guessing current_filter() is used to get the name of the filter for which the current execution is happening?

Answer 1

Hi @Raj Sekharan:

Looks good to me, but is wanting to know the current usage really your question or do you want to understand where current_filter() gets it's information from?

If the latter, here's basically what happens in all the different hook processing functions, e.g. do_action(), apply_filters(), do_action_ref_array(), apply_filters_ref_array() (greatly simplified, of course):

<?php
function <process_hook>($hook, $value) {
  global $wp_filter, $wp_current_filter;
  $wp_current_filter[] = $hook;  // "Push" the hook onto the stack.
  $value = call_user_func($wp_filter[$hook]['function'],$value);
  array_pop($wp_current_filter);
  return $value;
}

Then all that current_filter() does is retrieve the last hook "pushed" onto the global wp_current_filter array, i.e.:

<?php
function current_filter() {
  global $wp_current_filter;
  return end( $wp_current_filter );
}

Answer 2

In general—yes, this is a valid usage. If I were you I would pass different functions to the different filters and abstract the common parts in other function(s).

This way any of your function will do exactly one thing.