Question

It seems that string is reference, but copied by value

List<string> data = new List<string>();
string s = "a";
data.Add(s); // copy by value??
s = "b";
Console.WriteLine(data[0]); // "a"

It also seems that class is reference copied by reference

class boxstring { public string val; }
List<boxstring> data = new List<boxstring>();
boxstring s = new boxstring { val = "a" };
data.Add(s); // copy by reference, ok
s.val = "b";
Console.WriteLine(data[0].val); // "b"

Is there a simpler way to pass string into collection by reference without wrapping it into class? I’d like to pass object member into collection and if the object is changed, the collection should be also changed without writing extra code.

Answer 1

Strings are immutable. Whenever you assign new value to string variable, a new instance is created everytime that’s why you can’t see the updates in your collection.

However, .NET already provide mutable counterpart of string i.e. “StringBuilder“. This will work for you –

List<StringBuilder> data = new List<StringBuilder>();
StringBuilder s = new StringBuilder("a");
data.Add(s);
s.Clear();
s.Insert(0, "b");
Console.WriteLine(data[0]); // "b"