Re: Simple Question 3

[Jean-Marc Bourguet <jbourguet@free.fr>]

Stephen Cole wrote:
> 
> I would have thought that the compiler should just through the assignment X
> := Unit() out, because it does not statically match. I do not see why the
> compiler has the right to demand you write a Unit() function for the derived
> type. Is there a deeper reason why it does?

I think you did not understood what you did.  You created Unit as a primitive
operations of a tagged type which returns a value of this type.  The rules of
Ada imply that all non abstract derived types have to override the definition
of this function.

You probably didn't want to declare a primitive operation.  There are two
solutions: return a classwide type (so it will not return a value of the
type) or declare the function in another package (so it will not be a
primitive operation).

Declaring it in a nested package and providing a renaming will give you what
you though you had declared .

-- Jean-Marc