C＃默认情况下传递参数是ByRef而不是ByVal [英] C# Passing arguments by default is ByRef instead of ByVal

问题描述

我知道C＃中的默认值为ByVal。我在许多地方使用了相同的变量名，然后我注意到传递的值会发生变化并返回。我想我知道C＃的作用域机制错误。这里的公共许可证会覆盖本地的许可证值。我知道我可以轻松地在冲突中重命名变量名称，但是我想了解有关范围的事实。

I know the default is ByVal in C#. I used same variable names in many places and then I noticed passed values change and come back. I think I knew scope mechanism of C# wrong. Here public license overrides the local license values. I know I can easily rename the variable names in conflict but I would like to learn the facts about scope.

  public static class LicenseWorks
  {
     public static void InsertLicense(License license)
     {
        license.registered = true;
        UpdateLicense(license);
     }
  }

  public partial class formMain : Form
  {
     License license;

     private void btnPay_Click(object sender, EventArgs e)
     {
          license.registered = false;
          LicenseWorks.InsertLicense(license);

          bool registered = license.registered; //Returns true!
      }
  }    

更新： ve作为解决方案添加如下：

Update: I've added below as solution:

    public static void InsertLicense(License license)
    {

        license = license.Clone();
        ...
     }

推荐答案

参数通过值传递-但参数不是 object ，而是 reference 。该引用正在按值传递，但通过该引用对对象所做的任何更改仍将被调用方看到。

The argument is being passed by value - but the argument isn't an object, it's a reference. That reference is being passed by value, but any changes made to the object via that reference will still be seen by the caller.

这与 real 通过引用传递非常不同，后者对参数本身进行了更改，例如：

This is very different to real pass by reference, where changes to the parameter itself such as this:

 public static void InsertLicense(ref License license)
 {
    // Change to the parameter itself, not the object it refers to!
    license = null;
 }

现在，如果您调用 InsertLicense（ref foo），之后它将使 foo 为空。没有引用，就不会。

Now if you call InsertLicense(ref foo), it will make foo null afterwards. Without the ref, it wouldn't.

有关更多信息，请参见我写的两篇文章：

For more information, see two articles I've written:

• 在C＃中传递参数


• 引用和值（值类型和引用类型之间的差异）

• Parameter passing in C#
• References and values (the differences between value types and reference types)

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