Re: Is this expected behavior or not

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 15 Apr 2013 20:41:46 -0500, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:gj0dksp3fqws$.15ahjs6oqwquj.dlg@40tude.net...
>> On Fri, 12 Apr 2013 19:22:36 -0500, Randy Brukardt wrote:
> ...
>> And the solution is to remove Append? What would be a "good" design of
>> Unbounded_String and String such that you never mixed them? Is there any?
> 
> Not remove Append, but remove the version of Append that mixes two different 
> types.

OK, that is not serious.

> The only operations that change types should be explicit conversions 
> (possibly user-defined versions of that, using functions).

Conversions are mixed type operations per definition:

   function "+" (Value : String) return Unbounded_String;

is mixed, and additionally a multi-method if String and Unbounded_String in
the same hierarchy with "+" defined there.

>> You missing the main point that whatever difference Unbounded_String and
>> String may have, it is not a semantic difference. Both are different
>> implementations of the same thing. They are mixed right from the start.
> 
> Representation is an integral part of semantics.

I don't understand why you are using Ada then. There are lots of great
languages which pursue the principle that representation is semantics,
beginning with C.

> I strongly disagree that 
> they're representations of the same thing, because that would imply that 
> they do exactly the same thing for all operations -- and that's clearly not 
> true.

That is certainly true. All operations of these types deal with exactly
same thing called "string." Whatever difference existed is motivated solely
by implementation reasons, e.g. by memory management issues. These are
irrelevant to what string is: a sequence of code points with operations
like (), &, <, <=, Put_Line etc.

> I'm certain that nothing you want 
> to see will happen -- it isn't happening by magic.

Clearly so, when even separation of implementation and interface is no more
considered Ada's design principle.

I have no illusions. The trend is obvious when looking at Ada 2005 and
2012.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de