traits getProtection

[Jonathan M Davis]

On Tuesday, April 03, 2012 08:23:49 deadalnix wrote:
> Le 02/04/2012 22:59, Simen Kjærås a écrit :
> > On Mon, 02 Apr 2012 20:02:20 +0200, deadalnix <deadalnix at gmail.com> wrote:
> >>> Now, there are a number of people very unhappy about this state of
> >>> affairs and
> >>> want private to hide symbols as well (personally, I think that the
> >>> fact that
> >>> it makes private aliases effectively useless is reason enough to
> >>> seriously
> >>> reconsider the current behavior), but I don't know if there's any
> >>> real chance
> >>> of convincing Walter or not.
> >> 
> >> This would be a huge mistake. For instance, private method are
> >> sometime meant to be overridden in subclasses, which is impossible if
> >> symbol is inaccessible.
> >> 
> >> NVI for instance would be impossible in such a situation.
> > 
> > NVI is perfectly possible with protected.
> 
> You'll loose the ability to define a function, without being able to
> call it.

Except that that doesn't even actually work as discussed in this thread:

http://www.digitalmars.com/d/archives/digitalmars/D/Re_Module-
level_accessibility_118209.html#N118329

The derived class overrode the function, so it can call it. It may not be able 
to call the base class version, but it can call its own.

Sure, NVI is great, but it works just as well with protected. private doesn't 
actually prevent you from calling the function in the derived class, and even 
if it did, it's _not_ worth the cost of making private virtual by default. And 
as D lets the compiler control virtuality, unlike C++, it doesn't make any 
sense to make it so that the programmer can specifically make a private 
function virtual to work with NVI. So, it just makes more sense to use 
protected to do NVI.

Now, it may be different with interfaces. TDPL specifically talks about using 
private for NVI with _interfaces_, not classes. Doing that sort of thing with 
interfaces requires special treatment already, and it doesn't affect efficiency 
like making private always virtual would, so that should be okay. In the 
general case though, it's just far better to use protected to do NVI with 
classes and let private be non-virtual and therefore efficient by default rather 
than inefficient by default.

- Jonathan M Davis