So what does (inout int = 0) do?

[Andrei Alexandrescu via Digitalmars-d]

On 04/15/2016 12:23 AM, Jonathan M Davis via Digitalmars-d wrote:
> On Thursday, April 14, 2016 23:10:12 Andrei Alexandrescu via Digitalmars-d
> wrote:
>> Consider:
>>
>> https://github.com/D-Programming-Language/phobos/blob/master/std/range/primi
>> tives.d#L152
>>
>> There is no explanation to it in the source code, and the line blames to
>> https://github.com/D-Programming-Language/phobos/pull/2661 (irrelevant).
>>
>> Commenting it out yields a number of unittest compilation errors,
>> neither informative about the root of the problem and indicative as to
>> how the parameter solves it.
>>
>> There are two issues here:
>>
>> 1. Once a problem/solution pair of this degree of subtlety crops up, we
>> need to convince ourselves that that's sensible. If we deem it not so,
>> we look into improving the language to make the problem disappear.
>>
>> 2. There needs to be documentation for people working on the standard
>> library so they don't need to waste time on their own discovery process.
>>
>> We want Phobos to be beautiful, a prime example of good D code.
>> Admittedly, it also needs to be very general and efficient, which
>> sometimes gets in the way. But we cannot afford an accumulation of mad
>> tricks to obscure the large design.
>
> IIRC, the problem has to do with ranges of inout elements working correctly,
> which gets really funky, because inout is a temporary thing and not a
> full-on type constructor/qualifier. I believe that Kenji is the one that
> implemented the fix, and I think that he explained it in the newsgroup at
> some point. Certainly, there have been a few times that it's come up in
> D.Learn when folks ask what the heck it is, so there should be a few posts
> floating around with an explanation. This is the only useful post that I
> could find in a quick search though:
>
> http://forum.dlang.org/post/mh68p8$2p56$1@digitalmars.com
>
> inout attempts to solve a very real problem, but it does seem to be
> surprisingly hard to understand and use prooperly even though it's
> theoretically simple. And this bit with ranges is a quirk that I think very
> few people understand and remember. I usually forget exactly what it does
> when it comes up and have to try and dig through the newsgroup archives for
> a previous discussion on it.
>
> - Jonathan M Davis

I think we should deprecate inout. For real. It costs way too much for 
what it does. For all I can tell most of D's proponents don't know how 
it works. -- Andrei