Filter a pluggable function

Question

The following function is pluggable as it contains a filter :

// Make function pluggable/overwritable
if ( ! function_exists( 'wpsight_layout_images' ) ) {

    function wpsight_layout_images() {

        $layout_images = array(
            'show_on_single'         => true,
            'size_archive'           => 'post-thumbnail',
            'align_archive'          => 'left',
            'size_single'            => 'post-thumbnail',
            'align_single'           => 'left',
            'size_widget'            => 'post-thumbnail',
            'align_widget'           => 'left',
            'size_archive_listings'  => 'post-thumbnail',
            'align_archive_listings' => 'right',
        );

        return apply_filters( 'wpsight_layout_images', $layout_images );

    }

}

My question is the following. Lets say I need to change the value of the two last variables size_archive_listings and align_archive_listings using the filter. Do I have to copy over the whole function or can some variables be changed independently ? What is the proper of using add_filter from a child theme functions file in this situation ?

Answer 1

As noted in @Milo's comment, a function being "Pluggable" is entirely separate from it being filterable. A Pluggable function can be overridden wholesale, because of the if ( function_exists() ) conditional in which it's wrapped. A Plugin is filterable if its output is parsed through an apply_filters() call.

Since you only want to change a couple values in the returned array, you want to add a filter, rather than Plug the entire function.

Simply add the following in your Child Theme functions file:

function wpse117251_wpsight_layout_images( $layout_images ) {
    // Modify array values
    $layout_images['size_archive_listings'] = 'your-string-here';
    $layout_images['align_archive_listings'] = 'your-string-here';
    // Return the array
    return $layout_images;
}
add_filter( 'wpsight_layout_images', 'wpse117251_wpsight_layout_images' );

Answer 2

As Milo mentioned in his comment, the function is pluggable because it is wrapped in the function_exists() wrapper. To change the settings individually you would take advantage of the filter.

function wpa_117251( $layout_images ){
  $layout_images['size_archive_listings'] = 'medium';
  $layout_images['align_archive_listings'] = 'left';
  return $layout_images;
}
add_filter( 'wpsight_layout_images', 'wpa_117251' );