Re: Alleged GNAT bug

["A. Cervetti" <andrea.cervetti@gmail.com>]

> 
> I state that a legal program fails with a compiler error message.
> 
> But please confirm if my program (see above URL) is really legal. Maybe I 
> mistake?

No, it is not.

The reason is not obvious and a little convoluted (like your program too) and depend upon the freezing rules (arm 13.14)
Anyway the reference to System.ads in the error message is misleading.

In the generic package With_Finalization you derive the type Derived from the formal Base type. Derived is a record extension (although null) of the base type.

This means that, when you instantiate the package the actual Term_Type_Without_Finalize is frozen (13.14.7).

The compiler tries to create a dispatch table for the primitive operation of the type.

Get_Literal is a primitive operation so it is frozen too (13.14.15 1/3) but the return type Term_Literal_Value is still incomplete (7.3.5)

The ARM is not explicit about this (as far as I know, any language lawyer out there?) but the reason of the error is as I said.

To avoid the error you should instantiate the package Finalizer after the completion of Term_Literal_Value.

if you need visibility of Term_Type you can declare it as private too.

....
   type Term_Type is private;

private

   type Term_Literal_Value is null record;

   package Finalizer is new Term_Handled_Record.With_Finalization(Term_Type_Without_Finalize);

   type Term_Type is new Finalizer.Derived with null record;
....


This works.

A.