Decode JSON into a specific class

json_decode_class.php

<?php

function deep_copy_and_validate_object($source, $destination)
{
    $reflectionClass = new \ReflectionClass($destination);
    foreach ($reflectionClass->getProperties() as $reflectionProperty) {
        $propertyName = $reflectionProperty->getName();
        if (property_exists($source, $propertyName)) {
            $propertyValue = $source->$propertyName;

            $expectedClass = false;
            $expectedArray = false;
            $expectedType = false;

            $comment = $reflectionProperty->getDocComment();
            if (is_string($comment) && preg_match('~^(?:/\*|\s*)\*\s*@var\s+\$([^\[\]\s]+)(\[\])?\s+(\S+)~m', $comment, $match)) {
                if ($match[1] === $propertyName) {
                    $expectedArray = !empty($match[2]);
                    if (class_exists($match[3])) {
                        $expectedClass = $match[3];
                    } else {
                        $expectedType = $match[3];
                    }
                }
            }

            if ($expectedClass && is_object($propertyValue)) {
                if ($expectedArray) {
                    throw new \DomainException('Expected an array but got an object: ' . $propertyName);
                }

                $tempDestination = new $expectedClass;
                deep_copy_and_validate_object($propertyValue, $tempDestination);
                $propertyValue = $tempDestination;
            }
            else if ($expectedArray && is_array($propertyValue)) {
                if ($expectedClass) {
                    $tempArray = [];

                    foreach ($propertyValue as $tempSource) {
                        if (!is_object($tempSource)) {
                            throw new \DomainException('Array contains value that cannot be copied to annotated class');
                        }

                        $tempDestination = new $expectedClass;
                        deep_copy_and_validate_object($tempSource, $tempDestination);
                        $tempArray[] = $tempDestination;
                    }

                    $propertyValue = $tempArray;
                }
                else {
                    foreach ($propertyValue as $arrayValue) {
                        $actualType = gettype($arrayValue);
                        if ($actualType !== $expectedType) {
                            throw new \DomainException('Expected type ' . $expectedType . ' but got type ' . $actualType . ': ' . $propertyName);
                        }
                    }
                }
            }
            else if ($expectedClass || $expectedArray) {
                $actualType = gettype($propertyValue);

                if ($expectedClass) {
                    throw new \DomainException('Expected an object but got type ' . $actualType . ': ' . $propertyName);
                }

                if ($expectedArray) {
                    throw new \DomainException('Expected an array but got type ' . $actualType . ': ' . $propertyName);
                }
            }
            else if ($expectedType) {
                $actualType = gettype($propertyValue);

                if ($actualType !== $expectedType) {
                    throw new \DomainException('Expected type ' . $expectedType . ' but got type ' . $actualType . ': ' . $propertyName);
                }
            }

            $reflectionProperty->setAccessible(true);
            $reflectionProperty->setValue($destination, $propertyValue);
        }
    }
}

function json_decode_class(string $json, $destination, int $depth = 512, int $options = 0)
{
    $decodedObject = json_decode($json, false, $depth, $options);
    if (!is_object($decodedObject)) {
        return $decodedObject;
    }

    if (is_string($destination) && class_exists($destination)) {
        $destination = new $destination;
    }
    else if (!is_object($destination)) {
        throw new InvalidArgumentException('$class must be the fully qualified name of an existing class, or an object');
    }

    deep_copy_and_validate_object($decodedObject, $destination);

    return $destination;
}

class C2 {
    /** @var $qux string */
    private $qux;
}

class C1 {
    /** @var $foo C2 */
    public $foo;

    /** @var $bar[] C2 */
    public $bar;
}

$json = <<<EOJ
{
  "foo": {
    "qux": "Hello"
  },
  "bar": [
    {
      "qux": "X"
    },
    {
      "qux": "Y"
    },
    {
      "qux": "Z"
    }
  ],
  "does not exist": "does not get copied"
}
EOJ;

$obj = json_decode_class($json, 'C1');

var_dump($obj);