Re: Dispatching operations

[Maciej Sobczak <no.spam@no.spam.com>]

Jeffrey R. Carter wrote:

>> My confusion is that Op_B is private in P2. X is declared in P2 as 
>> well. In the above call, I'd expect P2.Op_B to be called (which is 
>> actually the case), but since everything is known statically, then I'd 
>> expect as well to get compile-time error due to the fact that P2.Op_B 
>> is private.
> 
> The important point is in 20.f: "The overriding declaration for P2.Op_B 
> is not visible in Main, so the name in the call actually denotes the 
> implicit declaration of Op_B inherited from T1."
> 
> Note that there is an implicit declaration of Op_B in P2 at the point of 
> the type extension.
> 
> Also note that X is not declared in P2; it is declared in Main.

Thanks, this clears thing a bit.

The question remains, though: how can I get compile error when calling 
private P2.Op_B?
If it's not possible, what's the point in making it private?

When I make this operation (P2.Op_B) public, the it hides the one 
inherited from P1.T1 and it is no longer possible to call P2.Op_B(Arg => 
X), because the named association of parameter is wrong. This means that 
by "promoting" something from private to public (!) in the given package 
I can break the existing client of that package.
This is a strange concept to me.


-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/