Le 29/11/2010 00:22, Christian Froeschlin a écrit :
> Le_Forgeron wrote:
> 
>> X & Y are both Policemen, but each one keep his/her/its gun protected.
> 
> But with this logic, the example Warp posted should also be forbidden.

Right, so you found a failure in the analogy when pushing it further
than intended.
I won't refine it, can you imagine policemen from the same specialised
activity sharing their gun ?

> 
> I didn't try it myself but if the behavior is as described in this
> thread it would mean protected access is restricted as follows:
> 
> Type/Instance This  Other
> 
> Parent        Ok    Fail
> 
> Same          Ok    Ok
> 
> Which I too find a bit odd.

Not so odd, if you consider that, from the point of view of knowing the
implementation, the failing case is just missing a friend to be ok;
Or turning it otherwise, the scope of calling other(B) when inside B is
ok, whereas the scope of calling other(A) when inside B is not.
(scope is different, hence the failure).

The sub-problem to forbid the warp's case would be if the called method
was a class method (not per instance, just per class)... it would
generate more problems.

Encapsulation principle: if you are the programmer in charge of B, you
do as you want with all the B, as long as it stays in B.

Protected:

    * Can be data and method members
    * Exactly same as private members for all practical purposes except
for the inheritance part
    * These members are inherited by a child of the class in which they
are declared
    * Their behaviour in the child class depends on how the inheritance
has been defined
    * If the inheritance is private these are private in the child
class; if it is public these are public in the child class and if the
inheritance in protected these are protected in the child class thus
allowing further inheritance.

Private:

    * Can be data or method members
    * Are accessible ONLY thru other methods of the same class where
they are declared
    * Cannot be accessed thru a class instance
    * Will not be inherited


-- 
Those who would give up Essential Liberty to purchase
a little Temporary Safety, deserve neither Liberty nor Safety.

Benjamin Franklin

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