What is PSR-11 standard?

The PSR-11 standard is a PHP-FIG (PHP Framework Interop Group) recommendation, officially titled “Container Interface”. It defines a common interface for dependency injection (DI) containers in PHP. This standard helps ensure interoperability between frameworks, libraries, and other components by providing a consistent way to retrieve objects or services from a container.

Key Features of PSR-11:

1. Purpose:
   It standardizes how objects or dependencies are fetched from a container, making it easier to swap or integrate DI containers.
2. Interface:
   The standard defines a single interface:

namespace Psr\Container;

interface ContainerInterface
{
    public function get(string $id);
    public function has(string $id): bool;
}

3. Methods:

• get(string $id):
  Retrieves an entry (object or service) from the container by its identifier. If the identifier does not exist, it should throw an exception.
• has(string $id): bool:
  Checks if the container has an entry for the given identifier.

4.Exceptions: PSR-11 also defines two exception interfaces:

• Psr\Container\NotFoundExceptionInterface:
  Thrown when the requested entry is not found.
• Psr\Container\ContainerExceptionInterface:
  Thrown when there is an error while retrieving the entry.

Why is PSR-11 Important?

• Interoperability:
  Developers can switch between DI containers or integrate different frameworks/libraries seamlessly.
• Standardized API:
  Since all PSR-11-compliant containers implement the same interface, you don’t need to learn a new API for each container.
• Easier Testing:
  You can use the same approach to mock or test dependency injection containers across different systems.

Example Usage:

Here’s how a PSR-11-compliant container might look in practice:

use Psr\Container\ContainerInterface;

class MyContainer implements ContainerInterface
{
    private $services = [];

    public function get(string $id)
    {
        if (!$this->has($id)) {
            throw new NotFoundException("Service {$id} not found.");
        }

        return $this->services[$id];
    }

    public function has(string $id): bool
    {
        return isset($this->services[$id]);
    }

    public function set(string $id, $service): void
    {
        $this->services[$id] = $service;
    }
}

// Usage
$container = new MyContainer();
$container->set('logger', new Logger());

if ($container->has('logger')) {
    $logger = $container->get('logger');
    $logger->log('PSR-11 is great!');
}

Popular Containers Supporting PSR-11:

• Symfony DependencyInjection
• Laravel’s Container
• PHP-DI
• Pimple