Re: Basic Explaination of OO in Ada

["Alex R. Mosteo" <devnull@mailinator.com>]

Ludovic Brenta wrote:

> Alex R. Mosteo wrote:
>> Just a note: although what Ludovic writes is right, and you can only have
>> vanilla arrays of definite types, you can have more sophisticated
>> containers (for example Ada.Containers.Indefinite_Vectors) that store
>> class-wide types in Ada 2005:
>>
>> package Pak_Vectors is
>>   new Ada.Containers.Indefinite_Vectors (Positive, Pak.T'Class);
>>
>> In this case, however, you store copies so some overhead can occur, but
>> in many cases it can be more convenient than starting to play with
>> pointers.
> 
> Doesn't Ada.Containers.Indefinite_Vectors have to declare a class-wide
> access type for its internal use? I'd guess so. But, it hides the
> access type from the user, and that's encapsulation at its best.

Yep, I suppose so (but I didn't looked for it).

> In Ada, one rarely needs access types at all. The only justification
> for declaring one is because you're doing some kind of dynamic data
> structure and allocating dynamically on the heap. With the standard
> Ada.Containers, you'd need access types even less often.

Agreed.

> That's why in my examples I did not declare an access type along with
> the tagged type (in package P); instead, I declared an access type in
> another package (package Collection) because that package absolutely
> needed one.

Ok, I missed your intention with the example here, so I was trying to make
clear that one shouldn't be too keen on jumping to access types :)