[swift-evolution] Nil coalescing operator precedence

[Xiaodi Wu]

On Wed, Jun 15, 2016 at 11:07 AM, Vladimir.S via swift-evolution <
swift-evolution at swift.org> wrote:

> >  If precedence between two operators is undefined, we cannot omit
> > parentheses.
>
> Hm.. Probably the initial problem could be solved with this? I.e. if we'll
> have *no* defined precedence between math operators and between ?? and
> between ?: (and probably something else?)  ?
>

Sorry, I don't see it. The initial question was about chaining of ??
operators. That's a problem with expectations about associativity and not
about precedence, right?


>
> As for rules of precedence, I think it is really not important what
> precedence will be assigned for ??/?: as in any case IMO most devs will not
> remember this for sure in situation when one need to write/read such
> complex expression.
>
> For me, probably I have some extreme opinion: if we have a mix of
> operators from different domains (math and ?? for example) we need
> parentheses to exclude any kind of ambiguity.
>
> On 15.06.2016 17:53, Антон Жилин wrote:
>
>> Nice points, I also think that unless operators are from the same domain,
>> more parentheses is better.
>> Other than that, what rules do we need? I can name these:
>> 1. Assignment operators have lower precedence than most operators
>> 2. Arithmetics has higher precedence than comparative and logical
>> operators. I don't think that ?? belongs to arithmetics, it's more like
>> control flow.
>> 3. Unary operators obviously have higher precedence than everything
>>
>> I didn't read se-0077 in details, so have no opinion. Probably you can
>>>
>> describe main ideas of it here in two words.
>> Replace numeric precedence with precedence relationships between pairs of
>> operators. If precedence between two operators is undefined, we cannot
>> omit
>> parentheses.
>>
>> My thought was basically: "parentheses between some operators must be
>> enforced by the language" <=> "SE-0077 is needed"
>>
>> - Anton
>>
>> 2016-06-15 17:17 GMT+03:00 Vladimir.S <svabox at gmail.com
>> <mailto:svabox at gmail.com>>:
>>
>>
>>
>>     On 15.06.2016 16:43, Антон Жилин via swift-evolution wrote:
>>
>>         `b + c * d / e` is not, obviously.
>>
>>
>>     obviously, for math operators it seems like we don't need any
>>     clarifications
>>
>>         `a ? b : c + x + y` -- I'd also say not, because, well, it's
>> ternary
>>         operator, the special case that everyone should know (otherwise it
>>         looks
>>         like a mess with ? and : operators).
>>
>>
>>     Yes, it's ternary operator.  But is it
>>     a ? b : (c + x + y)
>>     or
>>     (a ? b : c) + x + y
>>
>>     IMO ambiguous.
>>
>>         `a ?? x + y + z` -- maybe. If not for analogies with || and && and
>>         knowing
>>         about @autoclosure, I'd say that priority of ?? should be very
>> high.
>>
>>
>>     The same, is it
>>     a ?? (x + y + z)
>>     or
>>     (a ?? x) + y + z
>>
>>     ? I.e. I'm not asking, just show that the question is not if we know
>>     what does ?? mean, but how all the expression will be treated.
>>
>>     IMO it's totally false assumption that most of developers(and poor
>>     beginners) do remember the the correct precedence in such expressions
>>     and in most cases will not make a bug and so we should not require the
>>     parentheses. Imagine how each such expression will be crystal clear
>>     about the order of processing in *any* Swift source code you could
>> find
>>     anywhere. IMO this will be great advantage of the language.
>>
>>         Now that I think about it, if job of SE-0077 could be done with a
>>         linter,
>>         then... do we still need it?
>>
>>
>>     I didn't read se-0077 in details, so have no opinion. Probably you can
>>     describe main ideas of it here in two words.
>>
>>
>>         - Anton
>>
>>         2016-06-15 16:00 GMT+03:00 Vladimir.S <svabox at gmail.com
>>         <mailto:svabox at gmail.com>
>>         <mailto:svabox at gmail.com <mailto:svabox at gmail.com>>>:
>>
>>             As I understand, the question is if
>>
>>             `a ?? x + y + z`
>>             and
>>             `a ? b : c + x + y`
>>             (or `b + c * d / e`)
>>
>>             an "ambiguous case" ?
>>
>>
>>             On 15.06.2016 15:42, Антон Жилин via swift-evolution wrote:
>>
>>                 It's tempting to mention SE-0077 in this context. If it's
>>         accepted,
>>                 we will
>>                 be able to make omission of parentheses an error in
>>         ambiguous cases.
>>
>>                 - Anton
>>
>>
>>                 _______________________________________________
>>                 swift-evolution mailing list
>>                 swift-evolution at swift.org
>>         <mailto:swift-evolution at swift.org>
>>         <mailto:swift-evolution at swift.org <mailto:
>> swift-evolution at swift.org>>
>>                 https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
>>
>>
>>         _______________________________________________
>>         swift-evolution mailing list
>>         swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>         https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
>> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160615/7c9eddbc/attachment.html>