Dependency Injection in PHP (code to accompany https://youtu.be/TqMXzEK0nsA)

composer.json

{
    "autoload": {
        "psr-4": {
            "": "src/"
        }
    },  
    "require": {
        "php-di/php-di": "^7.0"
    }   
}

Container.php

<?php
    
class Container
{   
    private array $registry = [];

    public function set(string $name, Closure $value): void
    {
        $this->registry[$name] = $value;
    }

    public function get(string $class_name): object
    {
        if (array_key_exists($class_name, $this->registry)) {

            return $this->registry[$class_name]();

        }
    
        $reflector = new ReflectionClass($class_name);
        
        $constructor = $reflector->getConstructor();
                            
        if ($constructor === null) {
    
            return new $class_name;

        }

        $dependencies = [];

        foreach ($constructor->getParameters() as $parameter) {

            $type = $parameter->getType();

            $dependencies[] = $this->get((string) $type);
        }

        return new $class_name(...$dependencies);
    }
}

Database.php

<?php
    
class Database
{   
    public function __construct(private string $host,
                                private string $name,
                                private string $user,
                                private string $password)
    {
    }

    public function getConnection(): PDO
    {
        $dsn = "mysql:host={$this->host};dbname={$this->name}";

        return new PDO($dsn, $this->user, $this->password);
    }
}

index.php

<?php
    
require "vendor/autoload.php";
    
/*      
$container = new Container;
    
$container->set(Database::class, function() {
    
    return new Database(host: "",
                        name: "",
                        user: "",
                        password: "");

});
*/
$container = new DI\Container([

    Database::class => function() {

        return new Database(host: "",
                            name: "",
                            user: "",
                            password: "");
    }

]);

$repository = $container->get(Repository::class);

$data = $repository->getAll();

var_dump($data);

Repository.php

<?php
    
class Repository
{   
    public function __construct(private Database $database)
    {
    }                           
     
    public function getAll(): array
    {
        $pdo = $this->database->getConnection();
    
        $stmt = $pdo->query("SELECT * FROM product");

        return $stmt->fetchAll(PDO::FETCH_ASSOC);
    }
}