Re: was Re: Ada / C++ comparison paper anymore

[Patrick Hohmeyer <pi3_1415926536@yahoo.ca>]

Mark Lundquist wrote :

> No, but if I want to write
> 
>     procedure P2 is new P_Base (T2);
> 
> I can certainly do that, right?  And while P1 is primitive to T1 and P2 is
> not necessarily primitive to T2 (depending on the scope of the
> instantiation), an implicit instantiation is obviously not primitive
> either.
> I'm not seeing how my scheme weakens anything at all...  It just results
> in
> a lighter syntax.  Can you please be more specific about *exactly* what
> problems you see it causing, and how?  I would be genuinely interested to
> know...
> 

Ok, an exemple :

procedure X is

   generic
      type Number is range <>;
      type Num_Arr is array (Integer range <>) of Number;
   function Mean(A : Num_Arr) return Number;

   function Mean(A : Num_Arr) return Number is
      Sum : Integer := 0;
   begin
      for I in A'Range loop
         Sum := Sum + Integer(A(I));
      end loop;
      return Number(Sum/A'Length);
   end Mean;


type T_Employes is array(Integer range <>) of Natural;  -- employe numbers
type T_Employe_S is array(Integer range <>) of Natural; -- employe salaries

function Sal_Mean is new Mean(Natural,T_Employe_S);

Employes  : T_Employes(1..1000);
Employe_S : T_Employe_S(1..1000);
Mean_Sal  : Natural;

begin
   Mean_Sal := Sal_Mean(Employe_S); -- line 1
   Mean_Sal := Sal_Mean(Employes);   -- line 2
end X;

--end code -----------------------

First, I know that identifiers as similiar as Employes and
Employe_S are bad.
You can easly mix them and thats exactly the point here.

Line 1 is correct, we calculate the mean salary of our employes.
But Line 2 calculates the mean of the employe numbers.
This makes no sense, and thanks to Ada this dont even compile,
as I haven't defined the Mean function for the employe numbers.

But with your auto-instanciation, I simply would write Mean
and nobody catched the error. It compiles and even *runs* fine,
only the results are completly nonsense.

That's why I'm against auto-instantiations.

People make bugs. And everything that is transformed auto-magicly
helps bugs to survive longer.

-- 
Patrick Hohmeyer