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Newsgroups: comp.lang.ada
Subject: Re: GC in Ada
From: Georg Bauhaus <bauhaus@futureapps.de>
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Date: Fri, 09 Feb 2007 14:47:48 +0100
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Date: 2007-02-09T14:47:30+01:00
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On Thu, 2007-02-08 at 10:33 +0100, Markus E Leypold wrote:
> 
> Martin Krischik <krischik@users.sourceforge.net> writes:

> > Only Java has no const keyword. It is supposed to get one but how long
> > until it is actually used?
> 
> 
> Excuse me, but ... "a read only interface" means:
> 
>    (a) make all field of objects private 
>    (b) allow access only my methods

What Eiffel does by design.

>    (c) provide only Get_*-methods, no Set_*-methods

This lets programmers design type interfaces and wrappers so that
objects are effectively read-only.
Wouldn't it be nice to just export a constant view where
needed? Like C++'s const& or Ada's access-to-constant?
Or to have C++ const view and Ada in mode parameters
that extend to the referred object?

procedure a is

    type J is
        record
            x: Integer;
        end record;

    procedure nope(this: in J; new_x: Integer) is
    begin
        this.x := new_x; -- compile time error
    end nope;

begin
    nope(42);
end a;


struct J
{
  int x;
};

int main()
{
  J wj;
  const J rj = wj;

  wj.x = 42;
  rj.x = 42;  // compile time error
  return 0;
}