Ref keywords in C #

We have recently been asked for the correct use of the REF keyword, which we will illustrate here. In fact, to better understand the ref keyword, combining C + + code is easier. In addition, before starting our example, we need to explain a few things in advance:

There are two types of data in C #: A reference type (reference types) and a value type (values types). simple types (including int, long, double, etc.) and structs (structs) are value types, while other classes are reference types. A simple type replicates when the value is passed, and the reference type simply passes the reference, just like a pointer in C + +.

Note the difference between structs in C # and C + +. In C + +, structs and classes are essentially the same (except that default inheritance and default access are public rather private). In C #, structs and classes are very different. One of the biggest differences (which I personally think is also easy to overlook) may be that it is a value type, not a reference type.

The following code is an example of MSDN:

// cs_ref.cs
using System;
public class MyClass
{
　 public static void TestRef(ref char i)
　 {
　　 // The value of i will be changed in the calling method
　　 i = 'b';
　 }
　
　 public static void TestNoRef(char i)
　 {
　　 // The value of i will be unchanged in the calling method
　　 i = 'c';
　 }
　
　 // This method passes a variable as a ref parameter; the value of the
　 // variable is changed after control passes back to this method.
　 // The same variable is passed as a value parameter; the value of the
　 // variable is unchanged after control is passed back to this method.
　 public static void Main()
　 {
　　 char i = 'a';　　// variable must be initialized
　　 TestRef(ref i);　// the arg must be passed as ref
　　 Console.WriteLine(i);
　　 TestNoRef(i);
　　 Console.WriteLine(i);
　 }
}

It is easy to see that the output is:

b
b

So if you make some new changes to this example, change the value type (here with char) to a reference type, what effect does the program run?

// ----------------------------------------
// MyClass definition
public class MyClass
{
　 public int Value;
}
// ----------------------------------------
// Tester methods
public static void TestRef(ref MyClass m)
{
　 m.Value = 10;
}
public static void TestNoRef(MyClass m)
{
　 m.Value = 20;
}
public static void TestCreateRef(ref MyClass m)
{
　 m = new MyClass();
　 m.Value = 100;
}
public static void TestCreateNoRef(MyClass m)
{
　 m = new MyClass();
　 m.Value = 200;
}
public static void Main()
{
　 MyClass m = new MyClass();
　 m.Value = 1;
　
　 TestRef(ref m);
　 Console.WriteLine(m.Value);
　
　 TestNoRef(m);
　 Console.WriteLine(m.Value);
　
　 TestCreateRef(ref m);
　 Console.WriteLine(m.Value);
　
　 TestCreateNoRef(m);
　 Console.WriteLine(m.Value);
}