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Message-ID: <1235818.stAph9vF03@linux1.krischik.com>
From: Martin Krischik <krischik@users.sourceforge.net>
Subject: Re: where exactly c++,c fail and Ada gets thru'
Newsgroups: comp.lang.ada
Date: Wed, 26 Apr 2006 19:32:50 +0200
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Date: 2006-04-26T19:32:50+02:00
List-Id: <comp.lang.ada>

Maciej Sobczak wrote:

> Yes, classes are used to define new types. Is there any problem with
> this? It is also necessary in Ada if we want to do just a bit more of
> what is provided by type and subtype constructs.

Say:

type Y_Type is range 1 .. 10;
subtype X_Type is new x range 1 .. 5;

function F (X: X_Type) return Y_Type is
begin
  return X + 3;
end F

Now I would expect that an Ada compiler will not insert any runtime checks
as X + 3 is allways in the range of Y_Type. However:

function G (X: X_Type) return Y_Type is
begin
  return X + 7;
end G;

may well be outside the range of Y_Type and if so CONSTRAINT_ERROR will be
raised.

Now say we have a suitable C++ range template:

typedef range<int, 1, 10> Y_Type;
typedef range<Y_Type, 1, 5> X_Type;

Y_Type F (X_Type X)
  {
  return X + 3;
  }

Y_Type G (X_Type X)
  {
  return X + 7;
  }

Now anyone up to the challenge to define:

template <typename Base_Type, Base_Type First, Base_Type Last>
range::operator = (Base_Type right)

template <typename Base_Type, Base_Type First, Base_Type Last>
range::operator + (Base_Type right)

template <typename Base_Type, Base_Type First, Base_Type Last>
range::range (Base_Type right)

in such a way that it works like Ada - inclusive the *realistic* change that
the compiler will optimize away the range check in F ().

Martin
-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com