Re: A bunch of questions that come after "Hello world"

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

On 18 Nov 2002 02:24:46 -0800, wojtek@power.com.pl (Wojtek Narczynski)
wrote:

>Robert A Duff <bobduff@shell01.TheWorld.com> wrote in message news:<wcc7kfe8ma7.fsf@shell01.TheWorld.com>...
>
>> Part of the reason for these things is history.  Ada tasks were
>> originally just tasks -- there were no task types.  Similar to the way
>> packages are not "objects" -- there are no "package types".  This was
>> around 1980 or so.  Task types were added before the 1983 standard.
>> Protected types (added in Ada 95) were somewhat modeled after tasks,
>> and so inherited some of the oddities.
>
>Thanks for the explanation. I will have to keep the evolutionary
>nature of Ada syntax in mind.
>
>> Ada does not support multi-dispatch.  If you have two controlling
>> operands, they both have to have the same tag.
>
>What do you mean?
>
>procedure( X: Type1'Class; Y: Type2'Class);
>
>Compiles for me.

It is not the case. The case would be:

procedure Foo (X: Type1; Y: Type2);

Which will not compile. [An operation cannot be dispatching for two
different types.]  Your example does not dispatch, it is a class-wide
operation which is same for Type1, Type2 and all types derived from
them.

There is a more special case:

procedure Foo (X: Type1; Y: Type1);

This compiles and as long as the tags of X and Y are same works. If
they are not, Constraint_Error will propagate. One could call it
multiple dispatch, but then it is a very limited one.

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de