auto init & what the code means

[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. 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. There are straightforward cases where it's 
obvious that it's of benefit and obvious that the variable in question is being 
initialized, but beyond that, it really shouldn't be used.

- Jonathan M Davis