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From: osinski@hellgate.cs.nyu.edu (Ed Osinski)
Newsgroups: comp.lang.ada,comp.lang.c++
Subject: Re: ADA Objects  Help!
Date: 23 Jan 1995 23:47:49 GMT
Organization: New York University
Distribution: world
Message-ID: <3g1f75$fj1@thecourier.cims.nyu.edu>
References: <3f9g1u$j4m@nps.navy.mil> <D2H5un.FEr@nntpa.cb.att.com>
 <3flk3r$8qj@gdls.com>
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Xref: nntp.gmd.de comp.lang.ada:18219 comp.lang.c++:87738
Date: 1995-01-23T23:47:49+00:00
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In article <3flk3r$8qj@gdls.com>, wilkinso@gdls.com (Robert M. Wilkinson) writes:
|> In article <D2H5un.FEr@nntpa.cb.att.com>,
|> Kenneth Almquist <ka@socrates.hr.att.com> wrote:
|> >
|> >C++ has two procedure calling syntaxes.  It is possible to write either
|> >   display(myptr);
|> >or
|> >   myptr->display();
|>  
|> Please note that these have *entirely* different semantics; they are not
|> merely "two forms of syntax" for the same thing. 
|>  
|> >These both call a procedure, passing the value myptr as the argument.
|> >In contrast, Ada provides only a single procedure call syntax.
|> >
|> >When you declare a procedure in C++ you specify which syntax will be
|> >used to call the procedure.
|>  
|> Again, there is much more to it than just the syntax.  One is a member
|> function, the other is a plain-old function.  Big, big, difference. 

Sure, but why does the caller need to know which one is used?

|> >As a result, having the two syntaxes
|> >provides the following functionality:
|> >
|> >1.  Both Ada and C++ provide overloading, but in C++ it is possible for
|> >    two overloaded routines to have the same argument types as long as
|> >    the calling syntax is different.  The two calls to "display" which
|> >    appear above call different routines.
|>  
|> Of course they do.  One calls a member function, the other does not.  Think
|> of it as calling two functions with the same signature, but residing in
|> different packages.  
   ...
|> >My own opinion, formed before I knew anything about Ada 9X, is that this
|> >functionality is not useful, and thus having two syntaxes increases the
|> >complexity of the language without providing any corresponding benefit.
|>  
|> Perhaps you need a better C++ book.  If you cannot see the need for 
|> member functions, which is the heart and soul of C++, then you definitely
|> do not understand the language. 

But that is *not* what Kenneth said.  He simply doesn't see the need for two
different syntaxes.  Let me give you an example.  In C++, the *same* syntax is
used to call a virtual member function and a non-virtual member function.  Is a
virtual member function different from a non-virtual one in semantics?  Of
course they are, but that does not mean that there must be a different syntax
for calling them.  In fact, even C++ does let you use the non-member syntax for
*some* members.  They're called operators.  When you see

	a + b

and a and b are values of some user-defined type, the '+' could be a member
function, or a non-member function, but the syntax to invoke either is
identical.  Ada95 has one consistent syntax for calling both member functions
(or their nearest equivalent) and non-member functions.  This doesn't seem to
cause any problems.

|> -- 
|> ____________________________________________________________________________
|>   
|> Rob Wilkinson                                              wilkinso@gdls.com
|> ____________________________________________________________________________

-- 
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 Ed Osinski                  |
 Computer Science Department | "Do I know you? 
 New York University         |  And don't try to deny it!"
 E-mail:  osinski@cs.nyu.edu |                 Col. Flagg to Hawkeye
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