Project Elvis

[Patrick Schluter]

On Friday, 10 November 2017 at 19:59:29 UTC, meppl wrote:
> On Friday, 10 November 2017 at 05:23:53 UTC, Adam Wilson wrote:
>> On 11/6/17 12:20, Michael wrote:
>>> I can't quite see why this proposal is such a big deal to 
>>> people - as
>>> has been restated, it's just a quick change in the parser for 
>>> a slight
>>> contraction in the code, and nothing language-breaking, it's 
>>> not a big
>>> change to the language at all.
>>>
>>> On Monday, 6 November 2017 at 19:13:59 UTC, Adam Wilson wrote:
>>>> I am all for the Elvis operator, however I have two 
>>>> reservations about
>>>> it. The first is that I don't see much use for it without a
>>>> null-conditional. The second is that the current proposed 
>>>> syntax ?: is
>>>> MUCH to easily confused with ?.
>>>>
>>>> This is not easy to read: obj1?.obj2?.prop3?:constant.
>>>>
>>>> When designing syntax sugar, ergonomics are very important, 
>>>> otherwise
>>>> people won't use it. Microsoft spent a LOT of time and 
>>>> treasure to
>>>> learn these lessons for us. I see no reason to ignore them 
>>>> just
>>>> because "we don't like Microsoft"
>>>>
>>>> My proposal would be to copy what MSFT did, expect that I 
>>>> would I
>>>> would introduce both operators at the same time.
>>>>
>>>> Syntax as follows: obj1?.obj2?.prop3 ?? constant
>>>>
>>>> In practice I don't see much use of the idiom outside of 
>>>> null's. The
>>>> ONLY other thing that would work there is a boolean field 
>>>> and you
>>>> might as well just return the boolean itself because the 
>>>> return values
>>>> have to match types.
>>>
>>> I feel this is kind of embellished somewhat. When you write
>>>
>>>> This is not easy to read: obj1?.obj2?.prop3?:constant.
>>>
>>> you're not separating it out as you do when you write your 
>>> preferred
>>> version:
>>>
>>>> Syntax as follows: obj1?.obj2?.prop3 ?? constant
>>>
>>> How is
>>>
>>>> obj1?.obj2?.prop3 ?: constant
>>>
>>> not as easy to read as
>>>
>>>
>>>> obj1?.obj2?.prop3 ?? constant
>>>
>>
>> You're right, I didn't, that was intentional, because 
>> sometimes people write things like that. And it took a while 
>> for anyone to say anything about it. That is my point.
>>
>> But that's the thing. The ?? is significantly more obvious in 
>> the condensed version.
>>
>> This is something that a UX designer would recognize 
>> instantly, but human factors are very definitely not our 
>> strong skill as engineers. FWIW, my human factors experience 
>> comes from the deep study of airline crashes that I do as a 
>> pilot.
>>
>>> to me they are the same in terms of readability, only with ?? 
>>> you have
>>> greater chances of mistyping and adding a second ? in there 
>>> somewhere,
>>> whereas the ?: is just a contraction of the current syntax, I 
>>> really
>>> don't think it's that difficult, so I'm not sure what 
>>> people's hang-ups
>>> are, but I don't think the argument that ?? is easier to read 
>>> than ?:
>>> holds any weight here, because one *is* a change to the 
>>> language, and
>>> the other is a change to the parser and a contraction of a 
>>> standard
>>> convention.
>>>
>>
>> Two things. ?: is ALSO a change a to language (lexer+parser). 
>> As to the whole "it's no more likely to typo the colon than 
>> the question" argument, sure, but that depends on the keyboard 
>> layout more than anything else, what works for you may not 
>> work elsewhere. And in either case, it's an easy compiler 
>> error. So you don't win anything with the ?:, but you win 
>> readability with the ??. MSFT spends a LOT of time studying 
>> these things. It would be wise to learn for free from the 
>> money they spent.
>
> I still dont get your point. Are you sure `??` isn't more 
> readable for you, because you are just used to it?
>
> I think `?:` makes more sense to me and people who learn the D 
> programming language.
> At least As log as `null` becomes `false` and non-null-pointer 
> becomes `true`.
>
> If the operator shall check for `null` only, I would be fine 
> with `??`.
> Because then it wouldn't be a true shortcut of  
> https://dlang.org/spec/expression.html#ConditionalExpression  
> anymore
>
> I wonder what Mr. Bright and Mr. Alexandrescu would say about 
> the request to implement both, `??` and `?:`.

?: is a special case of the ternary operator of C. It is well 
established as extention in gcc and clang since forever. It is 
annoying that the C standard didn't incorporate it (afair because 
of Microsoft which didn't support it in Visual C) as it is quite 
practical.
Someone in the thread claimed its poor value because it only 
saved 1 character typing but that argument is idiotic as it is 
not used to replace
  a?a:b with a?:b but rather with something more like that

int code = holyshitbigassfunct(this, wathever, FOO, BAR);
if(!code)
   code = -1;
do_something(code);
with
do_something(holyshitbigassfunct(this, wathever, FOO, BAR) ?: -1);

Ok, I made up that example, but it is the kind of things that I 
was able to replace in my C project when I started to allow the 
Elvis operator.
I don't think that the benefit for D will be as spectacular as a 
lot of boilerplate can be avoided in other ways, but the message 
that I would like to bring over here, is that sometimes the 
benefit of a syntax sugar is not immediatly obvious when using 
the basic construct.