blocks|key|4444663|text|默认情况下，函数参数是常量。试图从函数体中更改函数参数的值会导致编译时错误。这意味着您不能错误地更改参数的值。如果希望函数修改参数值，并且希望这些更改在函数调用结束后仍然有效，请将该参数定义为in-out参数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4444664|​|4444665|📷|atomic|offset|length|4444666|4444667|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/f40854c5ec3e7a9e8a5050c54bb7b31c.png|imageAlt^0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@$G|V|H|W|1|X]]|A|$]]|$1|I|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q|R|-4]]]]

Function parameters are constants by default. Trying to change the value of a function parameter from within the body of that function results in a compile-time error. This means that you can’t change the value of a parameter by mistake. If you want a function to modify a parameter’s value, and you want those changes to persist after the function call has ended, define that parameter as an in-out parameter instead.

<a href="https://i.stack.imgur.com/uvuky.png" rel="noreferrer"><img src="https://i.stack.imgur.com/uvuky.png" alt="see image below for Description"></a>

blocks|key|4444686|text|inout参数允许我们更改值类型参数的数据，并在函数调用完成后保持更改不变。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4444687|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

inout parameter allow us to change the data of a value type parameter and to keep changes still after the function call has finished.

blocks|key|4444726|text|如果您使用类，那么，正如您所说的，您可以修改类，因为参数是对类的引用。但当您的参数是值类型时，这将不起作用(https://docs.swift.org/swift-book/LanguageGuide/Functions.html+-+In-Out+Parameters部分)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4444727|使用inout的一个很好的例子是这个(为CGPoints定义数学)：|4444728|func+%2B+(left:+CGPoint,+right:+CGPoint)+->+CGPoint+{
++return+CGPoint(x:+left.x+%2B+right.x,+y:+left.y+%2B+right.y)
}

func+%2B=+(left:+inout+CGPoint,+right:+CGPoint)+{
++left+=+left+%2B+right
}|code-block|syntax|javascript|4444729|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.swift.org/swift-book/LanguageGuide/Functions.html^0|1I|1Q|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

If you work with classes then, as you say, you can modify the class because the parameter is a reference to the class. But this won't work when your parameter is a value type (<a href="https://docs.swift.org/swift-book/LanguageGuide/Functions.html" rel="nofollow noreferrer">https://docs.swift.org/swift-book/LanguageGuide/Functions.html</a> - In-Out Parameters Section)

One good example of using inout is this one (defining math for CGPoints):

<pre><code>func + (left: CGPoint, right: CGPoint) -&gt; CGPoint {
 return CGPoint(x: left.x + right.x, y: left.y + right.y)
}

func += (left: inout CGPoint, right: CGPoint) {
 left = left + right
}
</code></pre>

blocks|key|4445114|text|基本上，当你想要处理变量的地址时，它很有用，它在数据结构算法中非常有用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4445115|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Basically it is useful when you want to play with addresses of variable its very useful in data structure algorithms

blocks|key|4444830|text|当使用inout参数swift+4.0work时|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4444831|class+ViewController:+UIViewController+{

++++var+total:Int+=+100

++++override+func+viewDidLoad()+{
++++++++super.viewDidLoad()
++++++++self.paramTotal(total1:+&total)
++++}

++++func+paramTotal(total1+:inout+Int)+{
++++++++total1+=+111
++++++++print("Total1+==>+\(total1)")
++++++++print("Total+==>+\(total)")
++++}
}|code-block|syntax|javascript|4444832|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

when use inout parameter swift 4.0 Work 

<pre><code>class ViewController: UIViewController {

 var total:Int = 100

 override func viewDidLoad() {
 super.viewDidLoad()
 self.paramTotal(total1: &amp;total)
 }

 func paramTotal(total1 :inout Int) {
 total1 = 111
 print("Total1 ==&gt; \(total1)")
 print("Total ==&gt; \(total)")
 }
}
</code></pre>

blocks|key|4445204|text|传递给Swift函数的所有参数都是常量，因此您不能更改它们。如果您愿意，可以将一个或多个参数作为inout传入，这意味着可以在函数内部更改这些参数，而这些更改会反映在函数外部的原始值中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4445205|例如，如果您想要将一个数字原地翻倍-即直接更改该值而不是返回一个新的值-您可以编写如下函数：|4445206|func+doubleInPlace(number:+inout+Int)+{
++++++number+*=+2
}|code-block|syntax|javascript|4445207|要使用它，首先需要将变量设置为整数-不能将常量整数与inout一起使用，因为它们可能会被更改。您还需要在参数名称之前使用&符号将参数传递给doubleInPlace，这是一个明确的识别，您知道它正被用作inout。|4445208|在代码中，您可以这样写:+var+myNum+=+10+doubleInPlace(number：&myNum)|4445209|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

All parameters passed into a Swift function are constants, so you can’t change them. If you want, you can pass in one or more parameters as inout, which means they can be changed inside your function, and those changes reflect in the original value outside the function.
For example, if you want to double a number in place – i.e. change the value directly rather than returning a new one – you might write a function like this:
<pre><code>func doubleInPlace(number: inout Int) {
 number *= 2
}
</code></pre>
To use that, you first need to make a variable integer – you can’t use constant integers with inout, because they might be changed. You also need to pass the parameter to doubleInPlace using an ampersand, &amp;, before its name, which is an explicit recognition that you’re aware it is being used as inout.
In code, you’d write this:
var myNum = 10
doubleInPlace(number: &amp;myNum)

When passing a class or primitive type into a function, any change made in the function to the parameter will be reflected outside of the class. This is basically the same thing an <code>inout</code> parameter is supposed to do.

What is a good use case for an inout parameter?

When to use inout parameters?

数据结构

Swift

将类或基元类型传递到函数中时，在函数中对参数所做的任何更改都将反映在类之外。这基本上与inout参数应该做的事情相同。inout参数最好的用例是什么？

问何时使用inout参数？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问何时使用inout参数？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问何时使用inout参数？
EN