Dispatching Example

["Ed Colbert" <colbert@abssw.com>]

Hi All,

Below is a simplified example from Richard Riehle's & my course on Ada.
GNAT v3.13p says that the call Is_Item is an mbiguous expression, and
ObjectAda v 7.2 says the statement is illegal based on LRM 5.2(6).  Both
Richard and I thought that the expression is tag indeterminate, LRM
3.9.2(6), and would static resolved, LRM 3.9.2(19).  Are Richard and I
missing something or are both compilers wrong?


package Dispatching_Examples
is
  type T1 is tagged private;
  function Is_Item return T1;

  type T2 is new T1 with private;
  function Is_Item return T2;

private
   -- full definition of T1 and T2
  type T1 is tagged null record;
  type T2 is new T1 with null record;
end Dispatching_Examples;


with Dispatching_Examples;
use Dispatching_Examples;
procedure Dispatching_Examples_Driver is
    A, B : T1;                    -- simple variables
    Q, R : T2;                    -- simple variables
    C    : T1'Class := A;     -- class-wide variable
    D    : T2'Class := R ;    -- class-wide variable
begin
    C := Is_Item ;              -- static resolution?
end Dispatching_Examples_Driver;