PHP - autoload extra code based on the WordPress template being used. Useful when separating your template functionality into multiple files.

php-wordpress-autoload-template-code.php

<?php

add_filter( 'template_include', array( $this, 'template_additional_code') );

/**
 * Load page specific code for each template.
 * 
 * Load additional code on a per template basis. Code in files are only useful for the particular template.
 *
 * @author De'Yonte W.<https://github.com/rxnlabs>
 * @return string Path to file used to render the post
 */
function template_additional_code( $page_template ){
  global $post;
  $template_filename = explode('/',$page_template);
  $template_filename = $template_filename[count($template_filename) - 1];
  // load the template specific for each template loaded
  if( file_exists(__DIR__.'/template-specific-code/'.$template_filename) ){
    require __DIR__.'/template-specific-code/'.$template_filename;
  }

  return $page_template;
}