Re: Unknown constraints and type composition

["Alejandro R. Mosteo" <alejandro@mosteo.com>]

On 14/06/2018 17:37, Alejandro R. Mosteo wrote:

Thanks everyone for your comments. I think every approach was different 
and had some good food for thought. It seems things where more or less as 
I figured but seeing how different people goes about it reassures me.

Alex.

> 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.