auto init & what the code means

[Jonathan M Davis]

On Sunday 26 December 2010 15:02:42 Daniel Gibson wrote:
> Am 26.12.2010 23:04, schrieb Jonathan M Davis:
> > On Sunday 26 December 2010 07:08:22 Andrei Alexandrescu wrote:
> >> On 12/26/10 8:54 AM, spir wrote:
> >>> On Sun, 26 Dec 2010 14:54:12 +0100
> >>> 
> >>> Andrej Mitrovic<andrej.mitrovich at gmail.com>   wrote:
> >>>> int i;    // auto-initialized to int.init
> >>>> int i = void; // not initialized
> >>> 
> >>> Thanks. Actually this solves my "semantic" issue, did not even think at
> >>> 'void'. (I will use it often). By the way, I don't want to play the
> >>> superhero with uninitialised values, simply sometimes the initial value
> >>> cannot be known at declare place.
> >>> 
> >>> 	int i;
> >>> 	if (foo)
> >>> 	
> >>> 	   i=0;
> >>> 	
> >>> 	else if (bar)
> >>> 	
> >>> 	   i=1;
> >>> 	
> >>> 	else
> >>> 	
> >>> 	   i=2;
> >>> 	
> >>> 	playWith(i);
> >> 
> >> Problem with = void for elaborate types is that you need to use
> >> emplace(&var, expr) to initialize them later.
> > 
> > And of course the _big_  problem with = void is that you're dealing with
> > garbage if you don't actually initialize the variable before you use it.
> 
> No, actually that's the *good* thing about = void. That initializing
> variables is default and you have this special syntax that may be used
> if you don't want initialization to happen.
> I really like how D does this: Make the safe thing default and the
> unsafe thing possible via more typing.
> 
> > It's a good
> > addition for performance-critical code, but in general, it's a _bad_ idea
> > to use. It solves a major problem which exists in C and C++ with regards
> > to undefined and undeterministic behavior. I'd get very worried if I
> > started seeing code that used it all over the place.
> 
> Yes, definitely. It's good for optimization and should be only used
> there, so the places where it's used instantly catch your eye.

Yes. I do think that D is doing this the correct way. What I'm saying is that 
using = void is a big problem if you do it often. The fact that = void results 
in the variable being garbage means that it should only be used if it needs to 
be used rather than normally. spir was talking about using it often in his code, 
which would be a _bad_ idea. I'm just saying that it should only be used when 
you need to use it, because it's behavior is very bad if misused. So, if code is 
using it frequently, that's a danger sign.

- Jonathan M Davis