C #. What will happen if the structure member is a reference?

As we all know, the structure (struct) is the value type, and the class (class) is the reference type. Now let's consider a question. If there is a reference type member in the structure, what will happen?
Now we have a structure oneline. Let's first introduce its features. It can be regarded as a line of string, but it also consists of several parts. Let me take an example: "ABCD", in some applications, I may need to know which elements the string consists of, whether it is A/B/C/D or ABC/d, considering that this line can be added, I used an arraylist to put these elements. I will know it when I call it later. Oh, it's ABC/d, instead of A/B/C/d, the corresponding processing is made;
Now let's look at my test code (with a debugger image ):
Oneline line_1 = new oneline ("test ");
Oneline line_2 = line_1;
Oneline line_3 = line_1.copy ();
Line_1.add ("new_line ");
Return;
If the reference type in the structure is a copy when the structure is assigned to another structure, line_2 and line_3 should be the same.
I took it for granted when I was writing a program .. as shown in the figure below, when you use line_2 in the code below, if you think it only contains the element "test, errors are inevitable.
After finding out this problem, I wrote a copy method to return the copy of this structure, and the problem never occurs again. We can see from the figure that line_3 is running as expected.

Finally, let me briefly describe what I learned about this exception ..
The Structure assignment should be equivalent to the superficial replication of the class (copying a value when a member is a value, and copying a reference when a member is a reference), rather than completely copying ..
Appledotnet@hotmail.com with oneline Structure Code see later

 

Public struct oneline
{
Int length;
String line;
Arraylist al;
Public oneline (string line) // Initialization
{
This. Line = line;
This. Length = line. length;
This. Al = new arraylist ();
This. Al. Add (line );
}
Public bool add (string newline) // Add a row
{
Foreach (Object OBJ in Al)
If (string) OBJ) = newline) return false;
This. Al. Add (newline );
This. Line = This. Line + newline;
This. Length = This. Line. length;
Return true;
}
Override Public String tostring ()
{
Return line;
}
Public oneline copy () // returns a copy.
{
Oneline OL = new oneline (this. Al [0]. tostring ());
For (INT I = 1; I <Al. Count; I ++)
Ol. Add (Al [I]. tostring ());
Return ol;
}
}