如何在Swift中获取数学PI常数 [英] How to get mathemical PI constant in Swift

问题描述

我正在尝试寻找一种方法来在我的Swift代码中包含PI常量.我已经在import Darwin的另一个答案中找到了帮助，据了解，我可以访问 C函数.

I am trying to find a way to include the PI constant in my Swift code. I already found help in another answer, to import Darwin which I know gives me access to C functions.

我还检查了Darwin中的Math软件包，并遇到了以下声明:

I also checked the Math package in Darwin and came across the following declaration:

var M_PI: Double { get } /* pi */

所以，我假设有一种在代码中使用PI的方法，我只是不知道如何 ...

So, I assume there is a way to use PI in the code, I just don't know how...

推荐答案

使用 Swift 3& 4 ，现在pi被定义为浮点数类型Double，Float和CGFloat的静态变量，因此不再需要特定的导入:

With Swift 3 & 4, pi is now defined as a static variable on the floating point number types Double, Float and CGFloat, so no specific imports are required any more:

Double.pi
Float.pi
CGFloat.pi

还要注意，.pi的实际类型可以由编译器推断.因此，在从上下文中清楚得知您正在使用的情况下，例如CGFloat，您可以只使用.pi(感谢@Qbyte和@rickster在注释中指出这一点).

Also note that the actual type of .pi can be inferred by the compiler. So, in situations where it's clear from the context that you are using e.g. CGFloat, you can just use .pi (thanks to @Qbyte and @rickster for pointing that out in the comments).

对于 Swift的较旧版本:

M_PI最初是在Darwin中定义的，但也包含在Foundation和UIKit中，因此导入其中任何一个都将为您提供正确的访问权限.

M_PI is originally defined in Darwin but is also contained in Foundation and UIKit, so importing any of these will give you the right access.

import Darwin // or Foundation or UIKit

let pi = M_PI

注意: 如评论中所述，pi也可以在Swift中用作 unicode 字符，因此您也可以这样做

Note: As noted in the comments, pi can also be used as unicode character in Swift, so you might as well do

let π = M_PI

alt + p是用于创建π unicode字符的快捷方式(在美国键盘上).

alt + p is the shortcut (on US-keyboards) that will create the π unicode character.

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