Re: "use" clauses and Ada 95 OOP

[schmid@alta.ide.com (Stephen Schmid)]

Mitch Gart wrote:
> 
> > To me the C++/Java syntax
> >
> >     x.func
> >
> > seems clearer than the Ada syntax in this case because what is being
> > called is the function that is associated with X at runtime, rather than
> > the function that comes from a given package.
> 

The above call in C++ does not mean that the function associated with
the class X will get called at runtime.  If x is a reference to a class,
and func is a virtual function, then x.func will 'dispatch' (to use an Ada
term) to the function corresponding to whatever class x happens to refer
to at runtime, which could be x or any subclass of x, so the situation is
similar to that which occurs in Ada.


> > In Ada 95 OOP we can have the situation where a call
> >
> >     pkg1.func(x)
> >
> > dispatches at runtime to
> >
> >     pkg2.func(x)
> >
> > It seems to me that this notation is misleading because a reader might
> > think that the function in pkg1 will be executed.
> >

I don't think this is misleading, and I would argue in favor of not using 
the use clause.  With the use clause, the reader has no clue as to
which function is being called without checking the context clauses, and
there is greater opportunity for error.  You are giving the reader _less_
information, which cannot be helpful.  Including the package name gives
the reader a starting point to determine what functions may be called at
runtime.  In a language with run-time dispatching, that is the most that
you can do.