swift 3 : how to handle precedencegroup now operator should be declare with a body?

Question

运算符的前 Swift 3 代码是:

infix operator × {associativity left precedence 150}

但是现在，根据 Xcode 8 beta 6，这会生成以下警告:

"operator should not be declared with body"

在目前不存在文档的情况下，使用 precedencegroup 谓词的正确方法是什么？

我已经试过了，但是没有用:

infix operator × : times
precedencegroup times {
     associativity: left 
     precedence: 150
}

Answer 1

根据 SE-0077 , 运算符的优先级不再由魔数(Magic Number)决定——相反，您现在使用 higherThan 和(如果该组驻留在另一个模块中)lowerThan precedencegroup 关系以定义相对于其他组的优先级。

例如(来自 evolution proposal ):

// module Swift
precedencegroup Additive { higherThan: Range }
precedencegroup Multiplicative { higherThan: Additive }

// module A
precedencegroup Equivalence {
  higherThan: Comparative
  lowerThan: Additive  // possible, because Additive lies in another module
}
infix operator ~ : Equivalence

1 + 2 ~ 3    // same as (1 + 2) ~ 3, because Additive > Equivalence
1 * 2 ~ 3    // same as (1 * 2) ~ 3, because Multiplicative > Additive > Equivalence
1 < 2 ~ 3    // same as 1 < (2 ~ 3), because Equivalence > Comparative
1 += 2 ~ 3   // same as 1 += (2 ~ 3), because Equivalence > Comparative > Assignment
1 ... 2 ~ 3  // error, because Range and Equivalence are unrelated

尽管在您的情况下，您的运算符似乎用于乘法，但您可以简单地使用标准库的 MultiplicationPrecedence 组，该组用于 * 运算符:

infix operator × : MultiplicationPrecedence

定义为:

precedencegroup MultiplicationPrecedence {
  associativity: left
  higherThan: AdditionPrecedence
}

有关标准库优先级组的完整列表，以及有关此更改的更多信息，请参阅 evolution proposal .