Re: Type declared in record?

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On Tue, 11 Nov 2003 22:43:15 GMT, Freejack <user@nospam.net> wrote:

>On Tue, 11 Nov 2003 17:08:56 -0500, Marius Amado Alves wrote:
>
>> On Tue, 2003-11-11 at 20:19, Freejack wrote:
>> 
>> This is not representative of any problem I can think of. Maybe you want
>> an array component, maybe a generic type, maybe something else. Please
>> rethink your problem and restate it.
> 
>Right now I'm working on Variant Records. For example...
>
>generic
>
>	type Item is private;
>
>package storage is
>
>	type Data_Structure is (Tree, Stack, List);
>	type Store(DatConf : Data_Structure) is private;
>private
>
>	type Node_Pointer is access Store;
>	
>	subtype BlockSize is Positive range 1..1024;
>
>	type Item_Array is array(BlockSize) of Item; 
>
>	type STree is record
>		Value 		: Item;
>		LPointer	: Node_Pointer;
>		RPointer	: Node_Pointer;
>		TPointer	: Node_Pointer;	-- Could be used for Threading, or NULL. --
>	end record;
>
>	type DLinkedList is record
>		Element		: Item;
>		Next		: Node_Pointer;
>		Prev		: Node_Pointer;
>	end record; 
>
>
>	type Store (DatConf : Data_Structure) is record
>		
>		case DatConf is 
>			when Tree =>
>				TreeConf : STree;
>					 
>			when Stack =>
>				StackConf : Item_Array;
>			
>			when List =>
>				ListConf : DLinkedList;
>		end case;
>
>	end record;
>
>
>end storage;
>
>
>This is all swell...but working with it would be a bit of a pain, so I'm
>toying around with other ideas that might give me better results.

Tagged types!

------------ Interface package ------------
generic
   type Item is private;
package Storage is
   type Store is
      new abstract Ada.Finalization.Limited_Controlled
         with private;
   function Get (Container : Store; ...) return Item is abstract;
   ... -- All other interface methods

private
   type Store is
      new abstract Ada.Finalization.Limited_Controlled
         with null record;
end Storage;

------------ An implementation using bounded arrays ---------
generic
   Max_Number_Of_Items : Positive;
package Storage.Bounded_Arrays is
   type Array_Store is new Store with private;
   function Get (Container : Array_Store; ...) return Item;
      -- Implements Get for Array_Store
   ...

private
   type Item_Array is
      array (Integer range 1..Max_Number_Of_Items) of Item;
   type Array_Store is new Store with record
      Size : Natural := 0;
      Data : Item_Array;
   end record;
end Storage.Bounded_Arrays;

------------ An implementation using double-linked lists ---------
....

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de