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

[Антон Жилин]

Inline:

2016-05-20 20:58 GMT+03:00 John McCall <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====

What's the purpose of equality relationships between precedence groups?
>

Agreed, will remove.


> 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?

- Anton
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