Bootstrap::cssClassFromString and Bootstrap::glyphiconFromString cannot handle render arrays

I think it makes more sense to check this in the methods that are consuming the passed value instead.

Furthermore, I also think it would be far easier to do something like the following so it encompasses everything (not just #markup):

// Check if provided value is a render array and
// prematurely render to extract string value.
$value = Element::isRenderArray($value) ? Element::create($value)->renderPlain() : $value;

Better title

My solution in #4 is all that is needed. A new "flatten" method is unnecessarily verbose. It implements type checking and "optimizations" that are not needed.

I just remembered that renderPlain actually returns an instance of \Drupal\Component\Render\MarkupInterface. So both values will need to be typecast to a string, which we can do like the following:

$string = '' + (Element::isRenderArray($string) ? Element::create($string)->renderPlain() : $string);

BTW - thank you for all your efforts for this great, alive and real object-oriented theme.

My pleasure :D

We should also change the method signature so it passes the string by reference, e.g. (&$string). That way, if it is a render array, it can set the necessary #printed property when it gets rendered (and doesn't render twice) later.

Awesome! Thanks @ytsurk, this is definitely on the right track.

I went ahead and made a few tweaks to the patch, mostly around documentation and introducing a new Bootstrap::toString() helper method (since this isn't likely the only place this will need it).