Question

Hi I know this is probably an obvious one, but Im just wondering how do I use my own function that I would create in functions.php instead of the default one.

To explain what Ive done, I went into wp-includes/general-templates.php and changed alot of the code around that was in get_calendar.

But upon reading more online I realized that I shouldnt have done this as as soon as the user updates to a new wordpress these lines may be overwritten.

I kept a copy of the original general-templates.php file. So im wondering how do I implement my new updated function instead of the one in general-templates.php?

Thank you

Answer 1

WordPress provides two different means to override default function output: pluggable functions and filters.

Pluggable Functions

A pluggable function (all of which live in pluggable.php), takes the following form:

if ( ! function_exists( 'some_function' ) ) {
    function some_function() {
        // function code goes here
    }
}

To override a pluggable function, simply define it in your own Plugin (or in your Theme’s functions.php file, as applicable):

function some_function() {
    // Your custom code goes here
}

Filters

A filter takes the following form:

function some_function() {
    // function code goes here
    return apply_filters( 'some_function', $output );
}

To override a filter, define a callback and add it to the filter:

function mytheme_filter_some_function( $output ) {
    // Define your custom output here
    return $output;
}
add_filter( 'some_function', 'mytheme_filter_some_function' );

Specifically for get_calendar()

If you look in source, you will see that the output for get_calendar() is passed through the get_calendar filter:

return apply_filters( 'get_calendar',  $calendar_output );

So you would simply write your own callback to modify $calendar_output, and hook it into get_calendar.

function mytheme_filter_get_calendar( $calendar_output ) {
    // Define your custom calendar output here
    $calendar_output = '';
    // Now return it
    return $calendar_output;
}
add_filter( 'get_calendar', 'mytheme_filter_get_calendar' );