Re: point by point advantages of Ada

["David Thompson" <david.thompson1@worldnet.att.net>]

James S. Rogers <jimmaureenrogers@worldnet.att.net> wrote :
...
> The solution for such a need is basically the same in both C++ and Ada.
> C++ provides no multiple dispatch capability. You must make such a
> function static, not virtual. In Ada you do the same thing. You simply
> define the procedure(s) taking more than one tagged type in another
> scope. An inner package is a common choice for another scope.
>
static is not the opposite of virtual, see below.  In C++ you can allow
the normal, implicit dispatch on one type (virtual) and do the other(s)
explicitly; or have a nonvirtual function that does both/all.  Yes in Ada
the options are effectively the same.

...
> What the original author does not mention is that C++ cannot dispatch
> based upon the return type of a function. This is done cleanly in Ada and
> not at all in C++ (or Java).
>
Ada uses return type to resolve overloading (at compile time), but
not to dispatch (possibly at run time).  (C++ and Java do neither.)

> In C++ you need to explicitly label a function as "virtual". The default is
> "static". In Java the default is the equivalent of virtual, and you must
> explicitly label "static" functions with the "static" keyword. In Ada
> functions are primitive to a type if they are declared in the same scope
> as the declaration of the type. That is, the "primitive" property is defined
> by scope, and not by the presence or absence of a reserved word.
> This is different from C++ and Java, but those languages also differ
> from each other. Such differences do not prove superiority.
>
C++ virtual and Java *final* are opposites, and yes the default is
reversed, but *static* (in both) is quite different -- it specifies methods
or variables which are per-class not per-instance.  (As well as having
other meanings in C++, and C, for things not in a class.)

--
- David.Thompson 1 now at worldnet.att.net