如何快速得到数学PI常数

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.

我正在寻找一种方法将PI常量包含在我的Swift代码中。我已经在另一个答案中找到了帮助，导入达尔文，我知道达尔文给了我C函数的访问权。

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

我还查看了达尔文的数学软件包，发现了以下声明:

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

var M_PI: Double {get} /* pi */。

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

所以，我假设在代码中有一种使用PI的方法，我只是不知道如何…

2 个解决方案

#1

235

With Swift 3, 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:

对于Swift 3, pi现在定义为浮点数类型Double、Float和CGFloat上的一个静态变量，因此不再需要特定的导入:

Double.pi
Float.pi
CGFloat.pi

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).

还要注意，编译器可以推断.pi的实际类型。因此，在使用CGFloat的情况下，您可以使用.pi(感谢@Qbyte和@rickster在评论中指出)。

For older versions of Swift:

对于较早版本的Swift:

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.

M_PI最初是在Darwin中定义的，但是也包含在Foundation和UIKit中，因此导入其中的任何一个都将使您获得正确的访问权限。

import Darwin // or Foundation or UIKit

let pi = M_PI

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

注意:正如注释中所提到的，pi在Swift中也可以用作unicode字符，所以您也可以这样做

let π = M_PI

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

alt + p是创建的快捷方式(US-keyboards)πunicode字符。

#2

import Darwin is not needed all M_x are visible with the import Foundation

导入Darwin是不需要的，所有M_x在导入基础中都是可见的

( Xcode Version 6.4 (6E35b) )

(Xcode版本6.4 (6E35b)

#1

235