Helper function for `is_initialized()`

is_initialized_helper.php

<?php

if (!function_exists('is_initialized')) {
    /**
     * Returns whether a property is initialized with a value.
     * @param string|object $object The class (name), that contains the property.
     * @param string $property The name of the property.
     * @return bool Whether the property is initialized with a value.
     */
    function is_initialized($object, string $property): bool {
        try {
            return (new ReflectionProperty($object, $property))->isInitialized(is_object($object) ? $object : null);
        } catch (ReflectionException $e) {
            return false;
        }
    }
}

You can use this inside a class for memoization.

class Controller
{
    public ?Service $service;

    public function getService(): ?Service
    {
        if (!is_initialized($this, 'service')) {
            $this->service = Container::get(Service::class); // either the service, or `null`
        }
        
        return $this->service;
    }
}

The object parameter can also be a string that references the class name. This is useful for testing static properties.