Why does adding a filter to 'the_title' break the server?

Question

I have this function that helps me nicely trim post titles:

namespace Helpers;
..
function _s_trim_post_title ( $length = null, $delimiter = null ) {
    $title          = get_the_title();
    $trimmed_title  = mb_strimwidth( $title, 
                                     0, 
                                     $length === null ? BIG_INT : $length, 
                                     '' // Won't use, bugs out.
                                    );
    $url            = esc_url( get_permalink() );

    if( strlen( $title ) == strlen( $trimmed_title ) ) {
        $delimiter = '';
    }

    $delimiter = $delimiter === null ? '' : (string)$delimiter;

    $output = '<h2 class="post-title"><a href="' . $url . '" rel="bookmark">' . $trimmed_title . $delimiter . '</a></h2>';

    return $output;
}

I call it, on content.php as follows:

echo Helpers\_s_trim_post_title(24, '...');

And I was thinking, how about of doing all that with a filter:

add_filter( 'the_title', 'Helpers\\_s_trim_post_title', 24, '...');

And now, on my content.php, I'd replace all that stuff with the simple:

the_title()

Unfortunately, this breaks the whole server and sends it into a continuous loop.

Why?

Answer 1

Here's the correct code snippet. Hope it'll work for you.

Helper function

namespace Helpers;
..
function _s_trim_content( $content = '', $length = null, $delimiter = null ) {
    $trimmed_content = mb_strimwidth( $content, 
        0, 
        is_null( $length ) ? BIG_INT : $length, 
        '' // Won't use, bugs out.
    );

    if ( mb_strlen( $content ) === mb_strlen( $trimmed_content ) || is_null( $delimiter ) ) {
        $delimiter = '';
    }

    return $trimmed_content . $delimiter;
}

the_title filter

add_filter( 'the_title', function( $title, $post_id ) {
    if ( 'post' === get_post_type( $post_id ) ) {
        return \Helpers\_s_trim_content( $title, 24, '...' );
    }
    return $title;
}, 10, 2 );

Answer 2

First of all, please try to understand how filter hooks work inside WordPress. These two functions will help you in this case apply_fitlers() and add_filter()

Then please check how the_title filter hook works and what it does and how it does.

the_title filter hook is used in lots of places. It's been used in front-end as well as backend and it only works with the title. But you added heading h2 tag and anchor a tag with it. You can use is_admin() conditional function to apply the filter only on front-end. So make sure your the_title filter callback only works with title and does not return any markup.

Your the_title filter hook callback Helpers\_s_trim_post_title() does not work with the arguments that it gets from the filter hook. And you called get_the_title() template tag inside the_title which became recursive call, an infinite loop! That's why your system isn't working as expected.