First Impressions!

[Patrick Schluter]

On Tuesday, 28 November 2017 at 04:17:18 UTC, A Guy With an 
Opinion wrote:
> On Tuesday, 28 November 2017 at 04:12:14 UTC, ketmar wrote:
>> A Guy With an Opinion wrote:
>>
>>> That is true, but I'm still unconvinced that making the 
>>> person's program likely to error is better than initializing 
>>> a number to 0. Zero is such a fundamental default for so many 
>>> things. And it would be consistent with the other number 
>>> types.
>> basically, default initializers aren't meant to give a "usable 
>> value", they meant to give a *defined* value, so we don't have 
>> UB. that is, just initialize your variables explicitly, don't 
>> rely on defaults. writing:
>>
>> 	int a;
>> 	a += 42;
>>
>> is still bad code, even if you're know that `a` is guaranteed 
>> to be zero.
>>
>> 	int a = 0;
>> 	a += 42;
>>
>> is the "right" way to write it.
>>
>> if you'll look at default values from this PoV, you'll see 
>> that NaN has more sense that zero. if there was a NaN for 
>> ints, ints would be inited with it too. ;-)
>
> Eh...I still don't agree. I think C and C++ just gave that 
> style of coding a bad rap due to the undefined behavior. But 
> the issue is it was undefined behavior. A lot of language 
> features aim to make things well defined and have less verbose 
> representations. Once a language matures that's what a big 
> portion of their newer features become. Less verbose shortcuts 
> of commonly done things. I agree it's important that it's well 
> defined, I'm just thinking it should be a value that someone 
> actually wants some notable fraction of the time. Not something 
> no one wants ever.
>
> I could be persuaded, but so far I'm not drinking the koolaid 
> on that. It's not the end of the world, I was just confused 
> when my float was NaN.

Just a little anecdote of a maintainer of a legacy project in C. 
My predecessors in that project had the habit of systematically 
initialize any auto declared variable at the beginning of a 
function. The code base that was initiated in the early '90s and 
written by people who were typical BASIC programmer, so the 
consequence of it was that functions were very often hundreds of 
lines long and they all started with a lot of declarations.
In the years of reviewing that code, and I was really surprised 
by that, was how often I found bugs because the variables had 
been wrongly initialised. By initialising with 0 or NULL, the 
data flow pass was essentially suppressed at the start so that it 
could not detect when variables were used before they had been 
properly populated with the right values the functionality 
required. The thing with these kind of bugs was that they were 
very subtle.

To make it short, 0 is an arbitrary number that often is the 
right value but when it isn't, it can be a pain to detect that it 
was the wrong value.