Unable to render page when 'meta title' page config param is set

[OlegIvan0v]

Preconditions

1. Magento 2

Steps to reproduce

1. Create a custom module with following controller:

use Magento\Framework\View\Result\PageFactory;

class SomeAction extends \Magento\Framework\App\Action\Action
{
    /**
     * @var PageFactory
     */
    protected $resultPageFactory;

    public function __construct(
        Context $context,
        PageFactory $resultPageFactory
    ) {
        parent::__construct($context);
        $this->resultPageFactory = $resultPageFactory;
    }

    public function execute()
    {
        /** $resultPage @var \Magento\Framework\View\Result\Page */
        $resultPage = $this->resultPageFactory->create();
        $resultPage->getConfig()->setMetadata('title', 'some meta title');
        return $resultPage;
    }
}

2. Open the created controller on storefront.

Expected result

Page is opened, its source contains <meta name="title" content="some meta title">

Actulal result

Error message: "Recoverable Error: Object of class Magento\Framework\View\Page\Title could not be converted to string..."

Additional info: the reason in that page config renderer tries to use page title object as meta title content (in \Magento\Framework\View\Page\Config\Renderer::processMetadataContent()).

Not sure if I would expect that getMetadata(); sets the title. Maybe it is omitted in the metadata array for a special purpose?
I cannot think of any but I have not much SEO knowledge :)
I'm just using $resultPage->getConfig()->getTitle()->set("FOO"); to set the title which works fine

[OlegIvan0v]

The problem is that we cannot set meta title of page using \Magento\Framework\View\Page\Config::setMetadata():

<meta name="title" content="Page title">

It's not related to page title:

<title>Page title</title>

We can set any other meta data, but not 'meta title' because during processing of meta data content magento invokes getter method of \Magento\Framework\View\Page\Config, which for 'title' data will be \Magento\Framework\View\Page\Config::getTitle(), which returns \Magento\Framework\View\Page\Title object, that is not converted to string.
This problem can be solved by specifying preference of \Magento\Framework\View\Page\Config\RendererInterface, but on my opinion we must be able to specify any meta content using default renderer class \Magento\Framework\View\Page\Config\Renderer.

[shiftedreality]

Correct way to setup title was specified by @xhallix

$resultPage->getConfig()->getTitle()->set("FOO");

But current behavior looks like issue. Setting metadata should have the same result for any meta name.

Created ticket MAGETWO-47807