An example of a rudimentary dependency injection container #php #dic

container.php

<?php

interface Database {}
class Mysql implements Database {}
class Postgresql implements Database {}

class Container
{
    protected $bindings = [];

    public function bind($interface, $concrete)
    {
        $this->bindings[$interface] = $concrete;
    }

    protected function resolveDependencies($dependencies)
    {
        $instances = [];
        foreach ($dependencies as $dependency) {
            $instances[] = $dependency->getClass() === null
                ? $this->resolvePrimitive($dependency)
                : $this->resolveClass($dependency);
        }
        return $instances;
    }

    private function resolvePrimitive($parameter)
    {
        if ($parameter->isDefaultValueAvailable()) {
            return $parameter->getDefaultValue();
        }

        return null;
    }

    private function resolveClass($parameter)
    {
        return $this->make($parameter->getClass()->name);
    }

    public function make($interface, $parameters = [])
    {
        if (!isset($this->bindings[$interface])) {
            throw new Exception('Binding not found');
        }

        return new $this->bindings[$interface]();
    }

    public function build($concrete)
    {
        $reflector = new ReflectionClass($concrete);
        $constructor = $reflector->getConstructor();

        if ($constructor === null) {
            return new $concrete();
        }

        if (!$reflector->isInstantiable()) {
            return null;
        }

        $dependencies = $constructor->getParameters();
        $instances = $this->resolveDependencies($dependencies);

        return $reflector->newInstanceArgs($instances);
    }
}

class Application extends Container
{
}

class Model
{
    private $db;

    public function __construct(Database $db)
    {
        $this->db = $db;
    }

    public function getDatabase()
    {
        return $this->db;
    }
}

$app = new Application();

$app->bind('Database', 'Mysql');
$model = $app->build('Model');
var_dump($model->getDatabase());