How to Pass External Variables to Filters/Actions

Question

I find myself needing to pass custom data to a filter provided by a 3rd party plugin. All of the ways I've seen to do this are really complicated and hard to wrap my head around.

Take this example:

$score = 42; //Some crazy calculation I don't want to repeat.

function add_score_to_title($title) {
    return 'Quiz Results (' . $score . '/') - ' . $title;
}

add_filter( 'aioseop_title_single', 'add_score_to_title');

How can I pass the $score variable to add_score_to_title()?

What I ended up doing was adding my variable onto the global $wp object. So you end up with this:

global $wp;
$score = 42; //Some crazy calculation I don't want to repeat.
$wp->some_random_name_for_score = $score;

function add_score_to_title($title) {
    global $wp;
    $score = $wp->some_random_name_for_score;
    return 'Quiz Results (' . $score . '/') - ' . $title;
}

add_filter( 'aioseop_title_single', 'add_score_to_title');

Dirty? Maybe. Simple? Yup! Any downsides to this technique? Please discuss.

UPDATE Here is the complete code in question -> http://pastebin.com/fkSXY04m

Answer 1

You have at least two options:

1. Globalize the desired variable, and then reference it inside the callback
2. Wrap the score calculation logic with a function, then reference it inside the callback

Globalize the Variable

<?php
global $score;
$score = 42; //Some crazy calculation I don't want to repeat.

function add_score_to_title($title) {
    global $score;
    return 'Quiz Results (' . $score . '/') - ' . $title;
}

add_filter( 'aioseop_title_single', 'add_score_to_title');
?>

Wrap the Score Calculation

If you only ever need the score calculation inside the filter, pull the logic into the callback itself:

<?php
function add_score_to_title($title) {
    $score = 0;
    $questions = get_quiz_result_questions();
    $total_questions = 0;
    foreach( $questions as $question ) {
        $order = $question->order;

        if( $order >= 100 ) {
            break;
    }

    if( $question->correct == $_POST['Q'][$order] ) {
        $score++;
    }
    $total_questions++;

    return 'Quiz Results (' . $score . '/') - ' . $title;
}

add_filter( 'aioseop_title_single', 'add_score_to_title');
?>

Better yet, you could wrap your score calculation in a function of its own, and then call that function inside your callback:

<?php
function wpse48677_get_score() {
    $score = 0;
    $questions = get_quiz_result_questions();
    $total_questions = 0;
    foreach( $questions as $question ) {
    $order = $question->order;

    if( $order >= 100 ) {
        break;
    }

    if( $question->correct == $_POST['Q'][$order] ) {
        $score++;
    }
    $total_questions++;
    $output['score'] = $score;
    $output['total_questions'] = $total_questions;

    return $output;
}

function add_score_to_title($title) {

    $score_results = wpse48677_get_score();

    $score = $score_results['score'];

    return 'Quiz Results (' . $score . '/') - ' . $title;
}

add_filter( 'aioseop_title_single', 'add_score_to_title');
?>

If you find you have problems referencing the $_POST object, you can also register your query variable and then use get_query_var() internally to get data:

function add_score_query_vars( $query_vars ) {
    $query_vars[] = 'Q';

    return $query_vars;
}
add_filter( 'query_vars', 'add_score_query_vars' );

With this in place, $_POST['Q'] can be replaced with get_query_var('Q').

Answer 2

function add_score_to_title($title = false) {
  static $score = false;

  if($score === false){
    // do calc
  }

  // plugin call (filter)   
  if($title !== false)
    return 'Quiz Results (' . $score . ') - ' . $title;

  // your call
  return $score;
}

Call the function anywhere in your script to get the score, it will only be calculated once.

Another way, using anonymous functions:

// do the calc
$score = 'xxx';

add_filter('aioseop_title_single', function($title) use($score){
  return 'Quiz Results (' . $score . ') - ' . $title;  
});

Answer 3

The following example sees the variable $my_calculation in the global scope, however from within our local function we need to declare global $my_calculation in order to access the variable in the global scope.

<?php 

    $my_calculation = 'result!';

    function my_function() {

        global $my_calculation;
        return $my_calculation;

    }

    add_filter( 'function_something_here', 'my_function');   

?>

This is just one way to go about it and it appears to be neat. Would this work for you?