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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: [OT] Re: Teaching new tricks to an old dog (C++ -->Ada)
Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
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Date: Thu, 10 Mar 2005 14:42:52 +0100
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Xref: g2news1.google.com comp.lang.ada:9037 comp.lang.c++:44961
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Date: 2005-03-10T14:39:34+01:00
List-Id: <comp.lang.ada>

On 10 Mar 2005 03:59:47 -0800, Alberto wrote:

> 1. Is Ada case-insensitive as Pascal? In that case, Ada==ADA

Well, Ada is not English. So Ada's rules about names are not applicable to
Ada's name. BTW, with C++ it is even worse: "C++" isn't a valid C++ name!
Though it nicely reflects the semantic of its usage: use what we have now,
it will be better later! (:-))

> 2. The C++ exception mechanism should be very similar to aDa's,
> because it was inspired partially from it [1].

Yes, but there is a sufficient difference. Ada's exceptions are values of
same predefined type. It has advantages and disadvantages. Being on Ada's
side I start with advantages and leave disadvantages to you:

1. 

exception
   when A => ...
   when B => ...

is strictly equivalent to

exception
   when B => ...
   when A => ...

2. C++ has no truly dynamic classes. But if it some time will, then how
would it deal with:

class BaseException
{
public :
   virtual void TellStories () = 0;
};

try
{
   ...
   { // Nested
      int I = 123; 
      class NewException : public BaseException
      {
      public
         void TellStories () { printf ("%d", I); }
      };
      throw NewException ();
   }
   ...
}
catch (BaseException& Error)
{
   Error.TellStories ();
}

3. The size of all exception objects has an upper bound.

> 3. Many of you want us to believe that ADa performs ra nge checking
> without loss of performance: it can be true at compile time with fixed
> ranges, but it can't definitely be done without chechinkg array bounds
> every time data is accessed if we don't know these bounds before
> compiling (e.g.: typical cases where dynamic allocation of memory is
> used)

But even then bounds checking is not needed for every access. Example:

procedure Dynamic (A : Some_Array) is
   subtype Index is Array_Index range A'Range;
   J : Index := A'First;

   for I in A'Range loop
      A (I) := .. -- No checks
      ...
      J := I;
   end loop;
   A (J) := ... -- Still no checks

C++ completely lacks the notion of constrained subtypes which makes the
above possible.

> 4. Also, some people wrote that C++ is bad because it is difficult
> (but not imposible, see Comeau C++) to follow 100% the Standard. The
> same can be said to adA, because at least if we own a compiler of the
> '83 Standard, we can't have the derivation a virtual function
> mechanisms, only interfaces (pure virtual classes)[2]. To me, it
> sounds reasonable to work with the last version of a compiler when
> possible.

As long as you have only one compiler vendor...

> 5. In fact, there are standard mechanisms (STL) to handle these array
> bound checking issues with ease.

They cannot be so effective as in Ada.

1. See above about constraining.
2. C++ is unable to allocate objects of indefinite size on the stack.

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