Re: was Ada 83 in fact object oriented ?

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

On Thu, 24 Sep 2015 15:23:57 -0700 (PDT), halfmaddad@gmail.com wrote:

> OO is a huge topic but I am wondering what are the basic requirements for
> a language to be said to support object orientation.

It is an unsettled question.

Usually dynamic polymorphism is considered essential for an OOPL.

In Ada 95 dynamic polymorphism was represented by tagged types and
primitive operations.

Ada 83 was said "object based", but not "object oriented."
 
> Ada 83 had packages and one package could be instantiated more then one time.

You mean generic packages. That is static polymorphism, usually, it is not
considered OO.

> Is it fair to say that basic class and methods were therefore supported? 

No. Because the key difference is that with static polymorphism you cannot
have a polymorphic object.

E.g. if you have a type declared within a generic package. Then each
instance of the package produces a new type. You cannot have an object
capable to hold values (or their equivalents as strong typing requires) of
both types. Therefore, there is no run-time class. The class of all
instances exists, but not in the language. Thus the language does not make
it.

> Do you have any examples of a language that just meets the threshold of being OO ?

From above, if you have polymorphic objects, the language is OO. Bordering
cases could be ones when some types have no classes or some classes have to
explicit types etc. Considering this, all languages are probably at the
threshold.

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