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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Quick question regarding limited type return syntax
Date: Thu, 31 Jul 2014 21:12:41 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:21368
Date: 2014-07-31T21:12:41-05:00
List-Id: <comp.lang.ada>

"Adam Beneschan" <adambeneschan@gmail.com> wrote in message 
news:bf9193d6-e1a8-4df3-8e36-b07a2b07655e@googlegroups.com...
...
>The effect is that subcomponents of Database that have default initial 
>values
>will be initialized, and subcomponents that don't have default initial 
>values
>will be initialized to garbage (except where the language says otherwise).
>That's really the same as your original example was trying to do.  I guess
>that explicitly putting "others => <>" in an aggregate is enough to
>convince GNAT not to think you were accidentally leaving something
>initialized to garbage.

I'd hope so: the syntax you gave says that you explicitly wanted something 
initialized to garbage. :-) [OK, explicitly default-initialized, whatever 
that does.] It's not a compiler's job to second-guess explicit instructions, 
programmers would get really annoyed if it did (and have a hard time getting 
anything done).

It's annoying that we couldn't get this "explicit default-initialization" 
syntax more widely used. I prefer to ensure that everything is properly 
initialized, but sometimes the default value is good enough. It would be 
nice to be able to specify that:

      Obj : My_Type := <>;
or maybe
      Obj : My_Type := (<>);

so that I could verify that every object is either initialized or explicitly 
left default initialized. Right now, I use a comment:

     Obj : My_Type; -- Default initialize is OK here, because ...

but it's hard for a tool to tell that everything is as it should be.

(We tried to allow "(<>)" for private types for Ada 2005, but ran into a 
number of problems that eventually led us to give up. Too bad, I don't think 
they were insurmountable, but we were running short on time.)

                                            Randy.