Project Elvis

[Adam Wilson]

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.


-- 
Adam Wilson
IRC: LightBender
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