what does " return $container->{$resource};" mean

Question

What does the brakets mean and where to read more

return $container->{$resource};

Answer 1

The brackets are to make use of variable variables. It makes it easier to distinguish between:

// gets the value of the "resource" member from the container object
$container->resource;

and

// gets the value of the "foo" member from the container object
$resource = 'foo';
$container->$resource;

You can read more here: http://php.net/manual/en/language.variables.variable.php