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From: Richard Riehle <richard@adaworks.com>
Newsgroups: comp.lang.ada
Subject: Re: "access constant" discriminant
Date: Sat, 15 Feb 2003 11:17:28 -0800
Organization: AdaWorks Software Engineering
Message-ID: <3E4E9248.3E71D984@adaworks.com>
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Xref: archiver1.google.com comp.lang.ada:34123
Date: 2003-02-15T19:08:28+00:00
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tmoran@acm.org wrote:

>
> why can't one say
>   type Lock_Type(Resource : access constant Resource_Type) ...
> Did the designers foresee and forestall my use with a function?

I raised an issue about this from time to time in this forum, but in
a sligthly different way.

We have,
                 type Reference is access all some-type;

and

                type Reference is acess constant some-type;

A function may have a an access parameter, which almost has in
semantics.   However,  it is possible to modify a component of
an access parameter.  I would like the option of preventing that
with,

               function F (X : access constant parameter-name) return
some-type;

This would make it illegal for the function to modify the components of
an access parameter.   Without the word constant, one could still modify
such components, but including it would make absolutely clear, in the
contract, that such side-effects would be impossible.

Richard Riehle