Re: operation can be dispatching in only one type

[Serge Robyns <serge.robyns@gmail.com>]

On Monday, 23 November 2015 12:29:55 UTC+1, Dmitry A. Kazakov  wrote:
> On Mon, 23 Nov 2015 02:23:57 -0800 (PST), Serge Robyns wrote:
> 
> > I'm facing an issue with Ada when it comes to use an operation on two
> > tagged types.
> 
> You can use tagged types, they cannot be dispatching arguments though. That
> is a big difference.
> 
> > However in C++ it does work as I expected.
> 
> C++ has no multiple dispatch either.

I'm not using multiple dispatching, I'm using "serial" dispatching.  What I'm trying to achieve is very close to the concept of a mix-in. The code in C++ is doing what I want to achieve.  Update the specific balance and the "parent" sum in a cheap and direct way.  Obviously there is a potential "bug" as I can pass any balance to the operation, including ones from another account.

> It is too late to declare a dispatching operation on T_Balance when you
> already used T_Balance as a type somewhere else, e.g. to instantiate a
> package.
> 

As I said that operation is not dispatching on T_Balance, the T_Account operation will be dispatching.

As with regards to callback constructs, this sounds like "ugly" workarounds IMHO.

This weekend I've been re-writing the complete core "class" hierarchy in C++11 and 1 XML SAX parser into Xerces as a test.  I still need to rewrite the existing business logic and decide on how to implement DAO for which I did a niece implementation in Ada (IMHO), as I can have mixture of data stores for different components.  The abstract interface is using multiple limited interfaces.  However I stumbled on something that looks very interesting: ODB (C++) https://en.wikipedia.org/wiki/ODB_%28C%2B%2B%29.  For Ada I did use GNATCOLL but was also looking at Gnoga as an alternative.

During that exercise I missed 2 major benefits of Ada.  Very strong typing, although C++11's "enum class" gives me the same when it comes to the primitive data types, i.e. scalars.  And last but not least it's readability.  I love the Pascal family syntax.  In my former C career I've suffered a lot of imbalanced '{}'. And I've been looking at C replacements since the early 1990's only to see that that syntax style is getting more and more spread. :-(

Having said that, I still didn't decide on which one to pursue, Ada 2012 or C++ 11 or 14.  One of the benefits of C++ is the very large collection of 3rd party libraries.  I do recognize the work of David Botton and yourself in that area.