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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: How to pass around access types to interfaces?
Date: Fri, 24 Oct 2008 06:55:14 -0700 (PDT)
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> > I assume this type declaration is in the main *procedure*. This
> > means that the type has a local scope and life, which prevents
> > converting its values to a more long-lived access type. Try
> > declaring Concrete_Type in a package; that makes it live as long as
> > the whole program, and should allow such conversions.
>
> Yeah, the declaration was in the main procedure. When moving it to a
> package everything works like it's supposed to. Thanks for your help.
>
> I guess I have still a lot to learn about Ada. I was just thinking
> about the lifetime of the object. It never occured to me that a type
> also has a lifetime.

This is one of the most complex areas of Ada; it defines the lifetime
of both objects and types in terms of "accessibility levels" (RM
3.10.2). This explains the error message "type in allocator has deeper
level than designated class-wide type".

Types can have a limited life time since they can be declared inside a
subprogram (or indeed in any block).

--
Ludovic Brenta.