如何在Swift 3中使用新的优先级组声明指数/幂运算符?

问题描述

Swift 3中针对Xcode 8 beta 6进行了更改，现在我无法像以前一样声明我的运算符的威力:

There's been a change in Swift 3 for Xcode 8 beta 6 and now I'm not able to declare my operator for power as I did before:

infix operator ^^ { }
public func ^^ (radix: Double, power: Double) -> Double {
    return pow((radix), (power))
}

我已经阅读了一下，并且有了新的变化在Xcode 8 beta 6中引入

I've read a bit about it and there's a new change been introduced in Xcode 8 beta 6

据此，我猜测我必须声明一个优先级组并将其用于我的运算符，如下所示:

From this I'm guessing I have to declare a precedence group and use it for my operator like this:

precedencegroup ExponentiativePrecedence {}

infix operator ^^: ExponentiativePrecedence
public func ^^ (radix: Double, power: Double) -> Double {
    return pow((radix), (power))
}

我要朝正确的方向努力吗?我应该在优先级组的{}中放入什么?

Am I going in the right direction to make this work? What should I put inside the {} of the precedence group?

我的最终目标是能够通过简单的操作员迅速进行电源操作，例如:

My final aim is to be able to make power operations with a simple operator in swift, e.g.:

10 ^^ -12
10 ^^ -24

推荐答案

您的代码已经编译并运行-如果您只是单独使用运算符，则无需定义优先级关系或关联性，例如在您给出的示例中:

Your code already compiles and runs – you don't need to define a precedence relationship or an associativity if you're simply using the operator in isolation, such as in the example you gave:

10 ^^ -12
10 ^^ -24

但是，如果您想与其他运算符一起使用，并且将多个指数链接在一起，则需要定义一个优先级关系，该优先级关系为 MultiplicationPrecedence和正确的关联性.

However, if you want to work with other operators, as well as chaining together multiple exponents, you'll want to define a precedence relationship that's higher than the MultiplicationPrecedence and a right associativity.

precedencegroup ExponentiativePrecedence {
    associativity: right
    higherThan: MultiplicationPrecedence
}

因此下面的表达式:

let x = 2 + 10 * 5 ^^ 2 ^^ 3

将被评估为:

let x = 2 + (10 * (5 ^^ (2 ^^ 3)))
//          ^^    ^^    ^^--- Right associativity
//          ||     \--------- ExponentiativePrecedence > MultiplicationPrecedence
//           \--------------- MultiplicationPrecedence > AdditionPrecedence,
//                            as defined by the standard library

有关标准库优先级组的完整列表，请参见演变提案.

The full list of standard library precedence groups is available on the evolution proposal.

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