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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: How do I write directly to a memory address?
Newsgroups: comp.lang.ada
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Date: Wed, 9 Feb 2011 09:43:45 +0100
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Date: 2011-02-09T09:43:45+01:00
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On Tue, 8 Feb 2011 13:48:29 -0800 (PST), Maciej Sobczak wrote:

> On Feb 8, 7:14�pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
> 
>>> q.e.d. what?
>>
>> 1. const T /= T
>> 2. not (const T <: T)
> 
> That's of course very interesting, but does not relate to the example
> that we are discussing.

It does, because const T is the type of the actual parameter and T is the
type of the formal parameter.

>>> Why do you want to substitute one type by another?
>>
>> Because one is passed as a parameter where another is declared, expected
>> and used. This is substitution.
> 
> No. According to the C standard (6.5.2.2/4) this is *assignment*.

Making local copies requires copy constructor. That's for sure. But this is
unrelated to the substitution, which is always there when you call a
subprogram with parameters and/or results.

> In Ada assignment looks like this:
> 
> declare
>    J : constant Integer := 7;
>    I : Integer;
> begin
>    I := J;  --  here
> 
>    --  and later, for example:
>    I := I + 1;
> end;
> 
> There is no substitution in the above code, at least as far as my
> definitions go. This is assignment.

In this example there is no call, except than the assignment operation.
Note that the assignment's implied profile is:

   procedure ":=" (Left : in out Integer; Right : Integer);

When J is substituted for Right there is no problem because the anonymous
types of "constant T" and "in T" are same in Ada.

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