Re: GC in Ada

[Martin Krischik <krischik@users.sourceforge.net>]

Markus E Leypold schrieb:

> Martin Krischik <krischik@users.sourceforge.net> writes:

>> Maciej Sobczak schrieb:

>> On my Weblogic course I could not stop shaking my head about all the
>> problems which brings the "all is pointer" concept of Java.

> Fortunately you can ignore this "all is pointer" by exposing only a
> read-only interface to the client and leaving the rest to the GC

Only Java has no const keyword. It is supposed to get one but how long 
until it is actually used?

> That
> feels exactly like passing records around with in, out and in/out.  I
> don't see the problem. Not to doubt your experience on this, but just
> because I'm curious: Can you provide a hint or example what the
> problems are?

I can give you the solution, which is not used all that widely because 
of the performance impact:

class X
   {
   Date date = new Date;

   Date
   get_Date ()
      {
      return new Date (date);
      }

   void
   set_Date (Date new_Date)
      {
      date = new Date (new_Date);
      }
   }

Got it? If get_Date would just return date it would return a modifiable 
pointer - which could be used and - well - modified almost everywhere.

As said the solution above is not used all that often and so the 
interesting part in the weblogic course was that the hard core java 
programmers had to learn that for remote call object those object might 
be copied behind the scenes and not passes by (non const) reference. And 
so to those objects modifications might be lost!

This was the moment where a hole horror scenario unfolded to me: 
programmers which actually modified objects returned by a geta function 
instead of using the appropriate seta function!

Martin