[swift-evolution] [Review] SE-0077: Improved operator declarations

[Matthew Johnson]

> On May 20, 2016, at 3:51 PM, John McCall <rjmccall at apple.com> wrote:
> 
>> On May 20, 2016, at 1:25 PM, Антон Жилин <antonyzhilin at gmail.com <mailto:antonyzhilin at gmail.com>> wrote:
>> Inline:
>> 
>> 2016-05-20 20:58 GMT+03:00 John McCall <rjmccall at apple.com <mailto:rjmccall at apple.com>>:
>> The transitivity rule plus the ability to define precedence relationships in both directions on a new precedence group allows a new precedence group to create a precedence relationship between existing unrelated precedence groups.  This should be forbidden.
>> 
>> Agreed, although there is an alternate solution to allow global-scope relationship definition.
>> Trying to write it formally:
>> 
>> ====begin====
>> Precedence relationships that, by transitivity rule, create relationship between two imported groups, is an error. Example:
>> 
>> // Module X
>> precedencegroup A { }
>> precedencegroup C { }
>> 
>> // Module Y
>> import X
>> precedencegroup B { precedence(> A) precedence(< C) }
>> 
>> This results in compilation error "B uses transitivity to define relationship between imported groups A and C".
>> The rationale behind this is that otherwise one can create relationships between standard precedence groups that are confusing for the reader.
>> ====end====
> 
> Seems good to me.

Would this be allowed if Module X already defined precedence group C > A (it would not be defining a *new* relationship between A and C in that case)?

> 
>> What's the purpose of equality relationships between precedence groups?
>> 
>> Agreed, will remove.
> 
> Ok.
>  
>> Your proposal should call out the special treatment of the Assignment and Ternary groups.
>> 
>> Do you mean that most operators should define greater precedence than Assignment / Ternary? Or there should be some other special treatment?
> 
> Just that they have implicit members.
> 
> John.

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