Creating a (global)-mapping

Question

I'm making a mapping between page-id's and category-id's, that's being used several places.

However I read from this post, that one should never use global variables if one could avoid it. But I would argue that this would be smart to have as a global variable, so it's not a function that should be executed several time (and iterate over several ID's every time).

But I'm unsure how to do this. Here's what I got:

/**
 * Should this be here, in order to make it global?
 */
$page_category_mapping = array();
global $page_category_mapping;


/** 
 * Building the mapping... 
 *
 * Should this tage the $page_category_mapping
 * as input? 
 */ 
function build_page_category_mapping(){
  // Going over all pages and maps them to a category
}
add_action( 'init', 'build_page_category_mapping' );


/**
 * I assume this function should take the array as input, right?
 */
function a_funtion_that_uses_the_mapping( $page_category_mapping ){
  echo '<pre';
  print_r( $page_category_mapping );
  echo '</pre';
}
add_shortcode( 'list_mapping', 'a_funtion_that_uses_the_mapping' );

Answer 1

I figured it out myself.

function generate_the_excluded_array() {

  global $excluded_pages;
  $excluded_pages = array('Foo', 'Bar');
}
add_action( 'after_setup_theme', 'generate_the_excluded_array' );

And then it can be 'imported' using the global, as such:

function example_shortcode_definition() {

  global $excluded_pages;
  echo $excluded[0];
}
add_shortcode( 'example_shortcode', 'example_shortcode_definition' );