Re: Clueless :)

[mheaney@on2.com (Matthew Heaney)]

Karel Miklav <karel@inetis.spppambait.com> wrote in message news:<qHEda.2435$wK6.104835@news.siol.net>...
> Learning Ada I'm playing with container libraries and there are some 
> things puzzling me. If I initialize a generic container with an abstract 
> data type, this container will copy the whole ADT through and forth on 
> every assignment and alike. Isn't this an overkill?

What do you mean by "copy the whole ADT" during assignment.  Types
don't get copied --only objects do-- so your question doesn't make any
sense as written.


> As I understand he gets in an iterator to increase, but he throws it 
> away and creates another one. Is it so cheap or am I missunderstanding 
> something about Ada compilers or something?

You're constructing a new iterator object from an existing iterator
object. Sort of like the function:

   class iterator {
   public:
      iterator succ() const;
   //..
   };

For example:

   iterator i;
   //...
   i = i.succ();

The reason it's written this way in Ada is because scalar types have a
built-in function that already does that:

   I : Integer;
   --...
   I := Integer'Succ (I);

John was just being consistent with the rest of the language.  The
Charles container library (modelled on the C++ STL) is implemented
similarly:

http://home.earthlink.net/~matthewjheaney/charles/


> And one more question about the concept supported by keywords bounded, 
> unbounded, dynamic, fixed-length etc. Like first I must admit I don't 
> get it; why is there a need for this in Ada, when in tens of other 
> languages I've seen there is not? 

Because you don't have "bounded" forms in C++; that is, an array
declared on the stack whose size is dynamic, i.e.

   void op(int n)
   {
      char str[n];  //not std c++
      //...

You can do this in Ada, in C99, and in g++.  For example:

   procedure Op (N : Natural) is
      S : String (1 .. N);
   begin
      --...

You typically need a "bounded" form in order to declare a stack-based
container, whose maximum number of items ("size") isn't know until
run-time:

   procedure Op (Size : Natural) is
      V : List_Subtype (Size);  --no dynamic allocation
   begin



> And why there are bounded, unbounded 
> and dynamic versions of Booch components but no polymorphic? 

Can't you just instantiate the container using an access type that
designates T'Class?