Re: Ada Distilled by Richard Riehle

[Shark8 <onewingedshark@gmail.com>]

On Friday, July 27, 2018 at 2:07:21 PM UTC-6, Dmitry A. Kazakov wrote:
> 
> Types algebra, yes. Most important type operations Ada lacks are:
> 
> - ad-hoc supertypes,
> - interface inheritance,
> - full MI,
> - full MD

Ad-hoc supertypes are, I think, a mistake. The value in SUBTYPE is that it is a singular set of restrictions [possibly null] placed upon it's "supertype". What this means is that for every SUBTYPE S there's an application of 'Base to get to the first subtype (Ada "TYPE") -- This means that the relation of TYPE/SUBTYPE can be graphed as a tree; if we introduce ad-hoc supertypes, we lose this property and now have to contend with a full many-to-many possibility TYPE-network rather than TYPE-tree. And I fail to see how this would be useful in-practice. (IOW, what is the real use-case? Does that use-case justify such an increase in complexity?)

I'm in agreement with interface-inheritance, I think: IIRC, you're referring to what is essentially my idea for "abstract interfaces" whereby we could define Ada's type-system in terms of the stated hierarchy; as per this picture:  https://en.wikibooks.org/wiki/Ada_Programming/Type_System#The_Type_Hierarchy -- exposing what is already fairly explicit in the LRM. 

Multiple Inheritance -- I'm not sure this is a good idea at all. Looking at C++ programmers and their experiences it seems to be more trouble than it's actually worth. (Interfaces aren't so bad, but can still conflict; Delphi has the IMPLEMENTS keyword that can be used for both disambiguation as well as delegation.) ...Why do you think Ada (or its successor) should have full MI?

Multiple Dispatch -- This one I can see having more usability than Multiple Inheritance.