Custom theme hooks / filters – passing arguments

I’m getting confused trying to implement these custom theme hooks. Trying to wrap my head around that.

I thought i understood this. but now after reading code for several hours; it’s made it worst.

How do i modify the argument being passed in the following?

functions.php

function theme_content() {
   do_action('theme_content'); // Initialize my custom hook
}


function theme_content_alter($arg) {
   // Do processing
   if (!$arg) {
     echo '<h2>default</h2>';
   }
   if ($arg == 'foo')  {
     echo '<div class="content">bar</div>';
   }

   echo apply_filters('theme_content','theme_content_alter', $arg);
} add_action('theme_content', 'theme_content_alter');

index.php

theme_content($arg = 'foo');

What i’m trying to achieve

Being able to override hooks and handle contextual processing inside a functions or a separate file from a require.

An example: on a front page i want theme_content() to have no sidebar but on a subpage it’ll contain a sidebar, etc. This could be expressed like so:

Is this the proper way to do this? I’ve tried to write it in my theme and haven’t been able to figure out why it’s not working. My arguments are not being passed in the parameters.

What i have done

Reviewed several threads on this SE and found them not very helpful for my context:

• Explanation for apply_filters function and its variables

• get_template_part vs action hooks in themes

• Difference Between Filter and Action Hooks?

If you want theme_content hook to run with arguments that you pass to theme_content() function you need to write it like this:

function theme_content($args) {

   do_action('theme_content', $args);
}