is my code to get CTFE instantiated object valid D ?

[chmike via Digitalmars-d-learn]

I need to create an app wide singleton instance for my class.
The singleton is immutable, but I want to allow mutable 
references to that singleton object so that I can do fast 'is' 
tests.

I declared this

class Category
{
      protected static immutable Category instance_ = new Category;
      Category instance() { return cast(Category)instance_; }
      ...
}

It compiles and the instance should be instantiated at compile 
time. I couldn't check yet.

The public interface of Category is designed so that the object's 
state can't be modified and thus remains immutable.

Is this code valid D or is the behavior undefined due to the cast 
?


A variant implementation would have a method that modifies the 
object but only internally and in a very controlled way to store 
strings in a cache for faster access. Would it still be valid D 
code ?