On Thu, 18 Oct 2018, G.B. wrote:

> There is a type declaration, I rememberd, in Ada, that
> does not allow any object of the type to be declared.

What, exactly, is the point of your question?

If you really want to define a type, which does not allow any object of 
that type to be declared, here is one such type:

   type Void is abstract tagged null record;

Note that objects of type Void'class can exist, but never, ever, any 
objects of type Void. Thus, for good reason the Ada compiler refuses to 
compile

   function Impossible(X: T) return Void;





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