ioc-container-example.php

<?php

class Container
{
    private array $instances = [];

    public function set(string $key, $value): void
    {
        if (is_string($value) || is_callable($value)) {
            $value = $this->resolve($value);
        }

        $this->instances[$key] = $value;
    }

    public function get(string $id)
    {
        if ($this->has($id)) {
            return $this->instances[$id];
        }
        try {
            return $this->instances[$id] = $this->resolve($id);
        } catch (ReflectionException $ex) {
            throw new Exception($ex->getMessage());
        } catch (Exception $ex) {
            throw new Exception($ex->getMessage());
        }
    }

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

    private function resolve($id)
    {
        if (is_callable($id)) {
            return $id();
        }
        return $this->instance(new ReflectionClass($id));
    }

    private function instance(ReflectionClass $class)
    {
        $constructor = $class->getConstructor();
        if (is_null($constructor) || $constructor->getNumberOfRequiredParameters() === 0) {
            return $class->newInstance();
        }
        $args = array_reduce($constructor->getParameters(), fn(array $carry, $arg) => (($type = $arg->getType()) ? $carry + [$this->get($type->getName())] : $carry), []);
        return $class->newInstanceArgs($args);
    }
}

class Test1 {
    public string $name = 'Default Test 1 Name';
}

class Test2
{
    public string $name = 'Default Test 2 Name';

    public function __construct(
        private Test1 $test1
    ) {}
}

class Test3
{
    public string $name = 'Default Test 3 Name';

    public function __construct(
        private Test2 $test2
    ) {}
}

$customTest1 = new Test1;
$customTest1->name = 'Custom Test 1 Name';

$ioc = new Container;
$ioc->set(Test1::class, $customTest1);

var_dump($ioc->get(Test3::class));

/*
PHP 8.1.x

Output:

object(Test3)#6 (2) {
  ["name"]=>
  string(19) "Default Test 3 Name"
  ["test2":"Test3":private]=>
  object(Test2)#11 (2) {
    ["name"]=>
    string(19) "Default Test 2 Name"
    ["test1":"Test2":private]=>
    object(Test1)#1 (1) {
      ["name"]=>
      string(18) "Custom Test 1 Name"
    }
  }
}

*/