Does C# pass a List<T> to a method by reference or as a copy? [duplicate]

Question

Taking my first steps in C# world from C/C++, so a bit hazy in details. Classes, as far as I understood, are passed by reference by default, but what about eg. List<string> like in:

void DoStuff(List<string> strs) {     //do stuff with the list of strings } 

and elsewhere

List<string> sl = new List<string>(); //next fill list in a loop etc. and then do stuff with it: DoStuff(sl); 

Is sl in this case passed by reference or is a copy made so that I'd need to redefine the worker function like

void DoStuff(ref List<string> strs)

to actually act on sl itself and not a copy?

Answer 1

It's passed by reference. List<T> is a class, and all class instances are passed by reference.

Answer 2

The behaviour is always the same: Passing by copying. In case the parameter is an object, the reference to the object is copied, so in fact you are working on the same object/list/whatever.