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From: Martin <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Saturation arithmetic woes.
Date: Wed, 29 Jul 2009 10:13:48 -0700 (PDT)
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Date: 2009-07-29T10:13:48-07:00
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On Jul 29, 6:03=A0pm, xorque <xorquew...@googlemail.com> wrote:
> generic
> =A0 type Discrete_Type is (<>);
>
> package Saturation is
>
> =A0 type Saturated_Type is new Discrete_Type;
>
> =A0 function "+"
> =A0 =A0 (Left =A0: Saturated_Type;
> =A0 =A0 =A0Right : Saturated_Type) return Saturated_Type;
>
> end Saturation;
>
> package body Saturation is
>
> =A0 function "+"
> =A0 =A0 (Left =A0: Saturated_Type;
> =A0 =A0 =A0Right : Saturated_Type) return Saturated_Type
> =A0 is
> =A0 =A0 Temp_Left =A0: constant Discrete_Type :=3D Discrete_Type (Left);
> =A0 =A0 Temp_Right : constant Discrete_Type :=3D Discrete_Type (Right);
> =A0 begin
> =A0 =A0 if Temp_Left + Temp_Right > Discrete_Type'Last then
> =A0 =A0 =A0 return Saturated_Type (Discrete_Type'Last);
> =A0 =A0 end if;
> =A0 =A0 if Temp_Left + Temp_Right < Discrete_Type'First then
> =A0 =A0 =A0 return Saturated_Type (Discrete_Type'First);
> =A0 =A0 end if;
>
> =A0 =A0 return Saturated_Type (Temp_Left + Temp_Right);
> =A0 end "+";
>
> end Saturation;
>
> with Saturation;
> with Ada.Text_IO;
>
> procedure Main is
> =A0 type T is range 1 .. 10;
>
> =A0 package T_Saturated is new Saturation (T);
> =A0 package IO =A0 =A0 =A0 =A0 =A0renames Ada.Text_IO;
> =A0 package TIO =A0 =A0 =A0 =A0 is new Ada.Text_IO.Integer_IO
> (T_Saturated.Saturated_Type);
>
> =A0 use type T_Saturated.Saturated_Type;
>
> =A0 X : constant T_Saturated.Saturated_Type :=3D 5;
> =A0 Y : constant T_Saturated.Saturated_Type :=3D 9;
> begin
> =A0 TIO.Put (X + Y); -- 10
> =A0 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