使用PHP类的WordPress函数文件

Question

I am currently creating a WordPress functions.php file based off this blog article - http://jonathannicol.com/blog/2014/06/22/organize-wordpress-functions-file/

All working fine so far, however I'm stuck when trying to add the Theme Logo function (https://codex.wordpress.org/Theme_Logo)

function theme_prefix_the_custom_logo() {
    if ( function_exists( 'the_custom_logo' ) ) {
        the_custom_logo();
    }
}

into the PHP class within the functions.php file.

I can't seem to call

<?php theme_prefix_the_custom_logo(); ?>

or

<?php $myTheme->theme_prefix_the_custom_logo(); ?>

from my front-page.php template file as i normally would. Any thoughts to where i should place this function within the class and how to make it available to template files within my theme?