在 C# 中按值传递引用类型
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Passing Reference types by value in C#
提问by
I want to pass a reference type by value to a method in C#. Is there a way to do it.
我想将引用类型按值传递给 C# 中的方法。有没有办法做到这一点。
In C++, I could always rely on the copy constructor to come into play if I wanted to pass by Value. Is there any way in C# except: 1. Explicitly creating a new object 2. Implementing IClonable and then calling Clone method.
在 C++ 中，如果我想通过 Value 传递，我总是可以依靠复制构造函数来发挥作用。在 C# 中有什么方法除了： 1. 显式创建一个新对象 2. 实现 IClonable 然后调用 Clone 方法。
Here's a small example:
这是一个小例子：
Let's take a class A in C++ which implements a copy constructor.
让我们以 C++ 中的类 A 为例，它实现了一个复制构造函数。
A method func1(Class a), I can call it by saying func1(objA) (Automatically creates a copy)
一个方法func1(Class a)，我可以通过说func1(objA)来调用它（自动创建一个副本）
Does anything similar exist in C#. By the way, I'm using Visual Studio 2005.
C#中是否存在类似的东西。顺便说一下，我使用的是 Visual Studio 2005。
回答by Bjarke Ebert
As already explained, there's no equivalent to C++'s copy constructors.
正如已经解释过的，没有等同于 C++ 的复制构造函数。
Another technique is to use a design where the objects are immutable. For immutable objects there is no (semantic) difference between passing a reference and a copy. This is the way System.String is designed. Other systems (notably functional languages) apply this technique much more.
另一种技术是使用对象不可变的设计。对于不可变对象，传递引用和副本之间没有（语义）差异。这就是 System.String 的设计方式。其他系统（特别是函数式语言）更多地应用这种技术。
回答by Marc Gravell
No, there is no copy-constructor equivalent in C#. What you are passing (by value) is a reference.
不，C# 中没有等效的复制构造函数。你传递的（按值）是一个引用。
ICloneableis also risky, since it is poorly defined whether that is deep vs shallow (plus it isn't very well supported). Another option is to use serialization, but again, that can quickly draw in much more data than you intended.
ICloneable也有风险，因为它是深还是浅的定义很差（而且它没有得到很好的支持）。另一种选择是使用序列化，但同样，它可以快速绘制比您预期的多得多的数据。
If the concern is that you don't want the method making changes, you could consider making the class immutable. Then nobodycan do anything nasty to it.
如果担心您不希望方法进行更改，则可以考虑使类不可变。那么没有人可以对它做任何讨厌的事情。
回答by Mohsen
take a look at this
看看这个
public class Product
{
public string Name;
public string Color;
public string Category;
public Product(Product o)
{
this.Name=o.Name;
this.Color=o.Color;
this.Category=o.Category;
}
// Note we need to give a default constructor when override it
public Product()
{
}
}
public Product Produce(Product sample)
{
Product p=new Product(sample);
p.Category="Finished Product";
return p;
}
Product sample=new Product();
sample.Name="Toy";
sample.Color="Red";
sample.Category="Sample Product";
Product p=Produce(sample);
Console.WriteLine(String.Format("Product: Name={0}, Color={1}, Category={2}", p.Name, p.Color, p.Category));
Console.WriteLine(String.Format("Sample: Name={0}, Color={1}, Category={2}", sample.Name, sample.Color, sample.Category));
回答by redspidermkv
According to this link (already posted): http://msdn.microsoft.com/en-us/library/s6938f28(VS.80).aspx
根据此链接（已发布）：http: //msdn.microsoft.com/en-us/library/s6938f28(VS.80) .aspx
Passing a reference type by value is shown below. The reference type arr is passed by value to the Change method.
按值传递引用类型如下所示。引用类型 arr 按值传递给 Change 方法。
Any changes will affect the original item unless the array is assigned a new memory location in which case, the change is entirely local to the method.
除非为数组分配了新的内存位置，否则任何更改都将影响原始项，在这种情况下，更改完全是方法本地的。
class PassingRefByVal
{
static void Change(int[] pArray)
{
pArray[0] = 888; // This change affects the original element.
pArray = new int[5] {-3, -1, -2, -3, -4}; // This change is local.
System.Console.WriteLine("Inside the method, the first element is: {0}", pArray[0]);
}
static void Main()
{
int[] arr = {1, 4, 5};
System.Console.WriteLine("Inside Main, before calling the method, the first element is: {0}", arr [0]);
Change(arr);
System.Console.WriteLine("Inside Main, after calling the method, the first element is: {0}", arr [0]);
}
}
In closing, for a more in depth discussion, see the post by Jon Skeet in this question:
最后，要进行更深入的讨论，请参阅 Jon Skeet 在此问题中的帖子：
