Should alias expand visibility?

[Tomek Sowiński]

W dniu 26.07.2010 22:56, Nick Sabalausky pisze:
> "Steven Schveighoffer"<schveiguy at yahoo.com>  wrote in message
> news:op.vggugam1eav7ka at localhost.localdomain...
>> On Mon, 26 Jul 2010 15:08:32 -0400, Tomek Sowinski<just at ask.me>  wrote:
>>
>>> Nick Sabalausky wrote:
>>>
>>>>> Sorry you had to go through that.  My post was an attempt at dry humor
>>>>> ;)
>>>>>
>>>>> -Steve
>>>>
>>>> Heh, now I get it too. Good one :)
>>>
>>> Now me too:) But let's stay on the path:
>>>
>>> private void foo();
>>> public alias foo goo;
>>>
>>> We gotta do something about this WTF. Either goo should be perfectly
>>> usable
>>> or the compiler shouldn't allow visibility expanding aliases. Which'd you
>>> pick?
>>
>> Serious now:
>>
>> Your simple example doesn't make any sense.  Why wouldn't you just make
>> foo public?  If it's publicly accessible through an alias, it's publicly
>> accessible.  I don't buy the "too hard to understand" argument.  Just
>> don't document the "private" members :)
>>
>> IMO, protection attributes applied to an alias make no sense whatsoever.
>> I don't think the above code should compile, except dmd accepts lots of
>> noop attributes...
>>
>
> I disagree. I think it's perfectly rational. Perhaps a better example than
> the above:
>
> private void foo_implA() {...}
> private void foo_implB() {...}
> private void bar_implA() {...}
>
> static if( isDerpDerpDerp )
> {
>      public alias foo_implA foo;
>      public alias bar_implA bar;
> }
> else
> {
>      public alias foo_implB foo;
>
>      // If isDerpDerpDerp isn't true, then 'bar' is logically equivilent
>      // to the faster foo_implB, so just use that:
>      public alias foo_implB bar;
> }
>
> I see no reason to disallow something like that.

Yes, or a real-life example (sorry for quoting myself, but seems 
Steven's joke overshadowed it :) ):

struct PermutationMatrixExpr(Permutation permut) {
     static if (permut == Permutation.RowWise) {
         alias byPermutationDim byRows;
         alias byPermutationOrthoDim byColumns;
     } else {
         alias byPermutationDim byColumns;
         alias byPermutationOrthoDim byRows;
     }

private:

// Definitions for byPermutationDim & byPermutationOrthoDim

}

>> Let me draw a parallel example:
>>
>> int x;
>> const alias x y;  // I want y to be a const view of x
>>
>> Does this make any sense?
>>
>
> Just because one particular attribute doesn't make sence doesn't mean they
> all don't make sence.

Amen.

Can anyone give a good counter-example when a public alias of a 
non-public symbol is evil?


Tomek