Private visible?

[Lucas Goss]

Walter Bright wrote:
> Lucas Goss wrote:
>> Walter Bright wrote:
>>>
>>> Sometimes it is valuable to be able to say "you can't do this 
>>> operation with this type". I don't see why this ability should be 
>>> restricted to C++.
>>
>> Can someone come up with an example or explain why this would be 
>> valuable? To make sure we're on the same page, we're talking about:
>>
>> ----
>> class Base {
>>   public:
>>     virtual int Number() = 0;
>> };
>> ...
>> class Child : public Base {
>>   private:
>>     int Number() { return 1; }
>> };
> 
> I think it's a bug that the compiler allows this. It should be illegal 
> code, because it breaks encapsulation.

Um, maybe I didn't make it clear enough, or maybe I'm not understanding. 
The above is C++ code that went with this code:

(1)
Child c;
int num = c.Number(); //error: cannot access private member

(2)
Child* cp = new Child();
num = cp->Number(); //error: cannot access private member

(3)
Base* bp = new Child();
num = bp->Number(); // num = 1

So the compiler does error with the first two attempts, but the third 
compiles and runs fine. I was just trying to find an example of 
'poisoning' a base class that you mentioned. To me it doesn't sound like 
very good practice (maybe that's why C# and I think Java disallow such 
practice). I just wanted to make sure I'm understanding correctly.

Lucas