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From: Mart van de Wege <mvdwege@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Confused about class-wide types
Date: Sun, 20 Mar 2016 14:58:46 +0100
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Date: 2016-03-20T14:58:46+01:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

>
> Ada has named types equivalence. Event_Ptr and Message_Event_Ptr are
> two independent types regardless what they point to. If you declared
>
Yes, that's what threw me off.

>    type Message_Event_Ptr is access Event'Class;
>
> It would not work. Event if you did
>
>    type Message_Event_Ptr is new Event_Ptr;
>
> It still would not.
>
> All this is unrelated to class-wide vs specific types.
>
> BTW, it is a bad idea to use pointers, as bad as using vectors for a
> FIFO or Unbounded_String to keep constant strings. To dynamically
> allocate Unbounded_String which contents is again dynamically
> allocated is quite bizarre. Pointers could be used with queues when
> messages are pre-allocated elsewhere, in order to avoid copying
> overhead.

Yeah, but when I want to have a number of different Event types with
some common operations that I want to store in a Vector, I either need
pointers, or, as Shark8 points out, an Indefinite_Vector, which I
overlooked.

Mart

-- 
"We will need a longer wall when the revolution comes."
    --- AJS, quoting an uncertain source.