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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada requires too much typing!
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Date: Thu, 10 Jun 2010 10:15:14 +0200
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Date: 2010-06-10T10:15:15+02:00
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On Wed, 9 Jun 2010 14:22:53 -0700 (PDT), Maciej Sobczak wrote:

> On 9 Cze, 16:29, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
> 
>>> What is the common base class/interface for C++ or Ada containers?
>>
>> generic
>> � �type Element is private;
>> package Generic_Stack is
>> � �type Stack is limited private;
>> � �...
>> end Generic_Stack;
>>
>> The common base is the [generic] interface of Stack, which all instances
>> share, which every programmer has in mind talking about stack.
> 
> Do you mean that every container supports push and pop operations
> (actually Append, Last_Element, Delete_Last, etc.)?

Yes.

>>> How can I use it?
>>
>> You cannot, which is the problem of generics.
> 
> Or maybe not generics in general, but the specific approach to
> generics that was chosen by Ada.
> Remember, in C++ this is not a problem:
> 
> #include <vector>
> #include <list>
> 
> template <class ContainerOfInts>
> void appendThreeInts(ContainerOfInts & c)
> {
>     c.push_back(7);
>     c.push_back(42);
>     c.push_back(123);
> }
> 
> int main()
> {
>     std::vector<int> vec;
>     std::list<int> lst;
> 
>     appendThreeInts(vec);
>     appendThreeInts(lst);
> }
> 
> The appendThreeInts function uses the implicit common interface, even
> though vector and list do not share anything explicitly.

You didn't use it. Nowhere in the program it was manifested. It appears
that the program "uses" this common interface. But this "use" is as virtual
as one by the hex code produced by the compiler. Similarly you could take
an int variable, put there 4 and claim that the variable is even, "per
use".  But it is not.

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