Re: Saturation arithmetic woes.

[Martin <martin.dowie@btopenworld.com>]

On Jul 29, 6:03 pm, xorque <xorquew...@googlemail.com> wrote:
> generic
>   type Discrete_Type is (<>);
>
> package Saturation is
>
>   type Saturated_Type is new Discrete_Type;
>
>   function "+"
>     (Left  : Saturated_Type;
>      Right : Saturated_Type) return Saturated_Type;
>
> end Saturation;
>
> package body Saturation is
>
>   function "+"
>     (Left  : Saturated_Type;
>      Right : Saturated_Type) return Saturated_Type
>   is
>     Temp_Left  : constant Discrete_Type := Discrete_Type (Left);
>     Temp_Right : constant Discrete_Type := Discrete_Type (Right);
>   begin
>     if Temp_Left + Temp_Right > Discrete_Type'Last then
>       return Saturated_Type (Discrete_Type'Last);
>     end if;
>     if Temp_Left + Temp_Right < Discrete_Type'First then
>       return Saturated_Type (Discrete_Type'First);
>     end if;
>
>     return Saturated_Type (Temp_Left + Temp_Right);
>   end "+";
>
> end Saturation;
>
> with Saturation;
> with Ada.Text_IO;
>
> procedure Main is
>   type T is range 1 .. 10;
>
>   package T_Saturated is new Saturation (T);
>   package IO          renames Ada.Text_IO;
>   package TIO         is new Ada.Text_IO.Integer_IO
> (T_Saturated.Saturated_Type);
>
>   use type T_Saturated.Saturated_Type;
>
>   X : constant T_Saturated.Saturated_Type := 5;
>   Y : constant T_Saturated.Saturated_Type := 9;
> begin
>   TIO.Put (X + Y); -- 10
>   IO.New_Line;
> end Main;
>
> saturation.adb:10:18: there is no applicable operator "+" for type
> "Discrete_Type" defined at saturation.ads:2
> saturation.adb:13:18: there is no applicable operator "+" for type
> "Discrete_Type" defined at saturation.ads:2
> saturation.adb:17:38: there is no applicable operator "+" for type
> "Discrete_Type" defined at saturation.ads:2
>
> I'm afraid I'm not well versed in the rules regarding operator name
> resolution...

generic
  type Discrete_Type is (<>);
  with function "+" (L, R : Discrete_Type) return Discrete_Type is <>;
package Saturation is

You need to provide a suitable "+" operator.

Cheers
-- Martin