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From: "Alejandro R. Mosteo" <alejandro@mosteo.com>
Newsgroups: comp.lang.ada
Subject: Unknown constraints and type composition
Date: Thu, 14 Jun 2018 17:37:26 +0200
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Date: 2018-06-14T17:37:26+02:00
List-Id: <comp.lang.ada>

I think I have read somewhere that types with unknown constraints are a 
good way of ensuring you (or your users) don't end with uninitialized values:

types Whatever (<>) is [limited] private;

function Create return Whatever;

This seems nice at first sight but when these types have any likelihood 
of ending as members of another type you will hit the "unconstrained 
member" problem.

A workaround then is to use a Indefinite_Holder, but that's an imposition 
on your clients (ugly). If your type is furthermore limited, then you 
must use pointers and consider providing controlledness and deallocation 
in the enclosing type (uglier).

Right now I'm on the point of a new design where I have many interrelated 
types that require initialization calls (it's a C binding). And, as 
always, I'm unsure of the way to go, or if I'm missing another technique 
without shortcomings. Your thoughts if you have any on this issue are 
much appreciated.

Alex.