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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: numbers as 'generics' parameters
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Date: Sat, 17 May 2008 09:47:46 +0200
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On Fri, 16 May 2008 13:52:23 -0700 (PDT), Maciej Sobczak wrote:

> On 16 Maj, 20:57, Gautier <gaut...@fakeaddress.nil> wrote:
> 
>> generic
>>    N: Integer;
>> package Fixed_size_vectors is
>>    Vector: array(1..N) of Float;
> 
> I guess:
>      type Vector is array (1..N) of Float;
> 
>> end;
> 
> How to write an operation that ensures *at compile time* that its two
> parameters are Fixed_size_vectors of equal N?
> Declare it in a child package? Is there any other option?

The first step is a bit tedious, but it is advisable to "rename" all formal
generic parameters within the package specification. [I don't know why
aren't they visible. That was a language design decision].

Anyway, here you go:

   generic
      N : Integer;
   package Fixed_Size_Vector is
      Size : Integer renames N;
      type Vector is array (1..N) of Float;
   end Fixed_Size_Vector;
   
   package V1 is new Fixed_Size_Vector (25);
   package V2 is new Fixed_Size_Vector (V1.Size);

> Similar question can be asked for (un)constrained and discriminated
> types. What are the options for such an operation?

You do it declaring a subtype, that constraints the discriminant or bounds.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de