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Functions, Scope, Includes, and Namespaces

Define a Function​

function myplugin_get_limit(): int {
    return 10;
}

In WordPress global function names must be unique. Prefix custom functions.

function myplugin_render_card(int $post_id): string {
    return '<h2>' . esc_html(get_the_title($post_id)) . '</h2>';
}

Parameters, Defaults, and Returns​

function myplugin_get_posts(int $limit = 10): array {
    return get_posts([
        'posts_per_page' => $limit,
        'fields'         => 'ids',
    ]);
}
function myplugin_get_post(int $post_id): ?WP_Post {
    $post = get_post($post_id);

    return $post instanceof WP_Post ? $post : null;
}

Anonymous Functions and Arrow Functions​

add_filter('the_title', function (string $title): string {
    return trim($title);
});

Use named callbacks if you may need to remove the hook later.

$ids = array_map(fn ($id) => absint($id), $raw_ids);

Arrow functions require PHP 7.4+.

Scope and Globals​

Variables inside functions are local. Use WordPress globals deliberately.

function myplugin_query_user_count(): int {
    global $wpdb;

    return (int) $wpdb->get_var("SELECT COUNT(*) FROM {$wpdb->users}");
}

Static Request Cache​

function myplugin_expensive_value(): string {
    static $value = null;

    if (null === $value) {
        $value = get_option('myplugin_value', '');
    }

    return $value;
}

Static variables cache only for the current request.

Includes​

require_once MYPLUGIN_DIR . 'includes/helpers.php';

Use require_once for required files and build paths from known constants.

Namespaces​

namespace MyPlugin\Admin;

function render_page(): void {
    echo '<div class="wrap"></div>';
}
\MyPlugin\Admin\render_page();

Importing Names​

namespace MyPlugin\Admin;

use WP_Post;

function inspect(WP_Post $post): string {
    return $post->post_title;
}

WordPress Callbacks​

Callback TypeExample
Function'myplugin_init'
Static method[MyClass::class, 'method']
Object method[$object, 'method']
Closurefunction () {}
add_action('init', 'myplugin_register_types');
remove_action('init', 'myplugin_register_types', 10);

The callback and priority must match when removing hooks.

Function Existence Guards​

if (! function_exists('myplugin_helper')) {
    function myplugin_helper(): string {
        return 'value';
    }
}

Prefer unique prefixes over relying on guards.

Common Pitfalls​

  • Generic function names that collide with plugins or themes.
  • Requiring files with fragile relative paths.
  • Hiding hook registration in unexpected includes.
  • Using anonymous callbacks when removal is required.
  • Reading request data inside helper functions with unclear side effects.
  • Adding type syntax unsupported by the target PHP version.