Symfony\Component\Form\PropertyPath::__construct PHP Method

    public function __construct($propertyPath)
    {
        if ($propertyPath === '' || $propertyPath === null) {
            throw new InvalidPropertyPathException('The property path must not be empty');
        }

        $this->string = $propertyPath;
        $position = 0;
        $remaining = $propertyPath;

        // first element is evaluated differently - no leading dot for properties
        $pattern = '/^((\w+)|\[(\w+)\])(.*)/';

        while (preg_match($pattern, $remaining, $matches)) {
            if ($matches[2] !== '') {
                $this->elements[] = $matches[2];
                $this->isIndex[] = false;
            } else {
                $this->elements[] = $matches[3];
                $this->isIndex[] = true;
            }

            $position += strlen($matches[1]);
            $remaining = $matches[4];
            $pattern = '/^(\.(\w+)|\[(\w+)\])(.*)/';
        }

        if (!empty($remaining)) {
            throw new InvalidPropertyPathException(sprintf(
                'Could not parse property path "%s". Unexpected token "%s" at position %d',
                $propertyPath,
                $remaining{0},
                $position
            ));
        }

        $this->length = count($this->elements);
    }