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August 13, 2012
Broken NVI support
Hello.
Please, put attention to following non-runnable due to linker 
errors sample http://dpaste.dzfl.pl/cad4b558.

I suspect that that NVI support is broken, because (my guess) 
linker assumes that interface should implement functions and 
doesn't look to class definition.

After reading relevant section in TDPL I found another issue: 
according to p.215 bar() and baz() may have (or even should) 
'override' specifier, but currently dmd rejects it. Moreover, dmd 
is irrelevant about whether 'bar' and 'baz' functions (within 
class definition) are specified with private keyword or not: is 
is a bug or intentional behavior?

If interface implements functions, which are called from another 
of interface's functions, linking goes fine. However, after 
rereading relevant TDPL paragraph and this Alexandrescu post [1] 
I think that the trick is that functions 'bar' and 'baz' are 
implemented *not* in interface but in class-implementer.

Furthermore, if function declarations are converted to empty 
definitions keeping the same class definitions, dmd accepts this 
ambiguity (class A.bar() and interface I.bar()) and gives 
priority to interface's functions on calling them.

So, is this a bug or my NVI misunderstanding is wrong and what is 
D design policy in this issue?

[1] 
http://digitalmars.com/d/archives/digitalmars/D/The_Non-Virtual_Interface_idiom_in_D_96739.html
August 13, 2012
Re: Broken NVI support
On Monday, 13 August 2012 at 18:48:09 UTC, Maxim Fomin wrote:
> Hello.
> Please, put attention to following non-runnable due to linker 
> errors sample http://dpaste.dzfl.pl/cad4b558.

[quote]
interface I
{
    private:
        void bar();
        void baz();
    final void foo()
[/quote]

 Isn't it in the specs that overriding methods need to be public 
functions? And interfaces are effectively for public interface 
only so there shouldn't be any private methods? I mean, what's 
the point in mentioning bar and baz if you can't call them? Or 
even foo in this case....
August 13, 2012
Re: Broken NVI support
On Mon, 13 Aug 2012 20:48:07 +0200, Maxim Fomin <maxim@maxim-fomin.ru>  
wrote:

> Hello.
> Please, put attention to following non-runnable due to linker errors  
> sample http://dpaste.dzfl.pl/cad4b558.

As Era pointed out, private functions in D are implicitly final, i.e.
not overridable. Change all instances of 'private' to 'protected',
and Bob is your proverbial uncle.

-- 
Simen
August 13, 2012
Re: Broken NVI support
On Monday, August 13, 2012 20:48:07 Maxim Fomin wrote:
> So, is this a bug or my NVI misunderstanding is wrong and what is
> D design policy in this issue?

Currently, only public and protected functions are ever virtual:

http://d.puremagic.com/issues/show_bug.cgi?id=4542

This may or may not change for interfaces in order to match TDPL, but I 
wouldn't expect it to ever change for classes. You should be able to do NVI 
just fine with protected.

- Jonathan M Davis
August 14, 2012
Re: Broken NVI support
Thanks for replies, will use protected.
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