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

c# pass-by-reference pass-by-value
Scre picture Scre · May 6, 2014 · Viewed 46.1k times · Source

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

Adrian Ratnapala picture Adrian Ratnapala · May 6, 2014

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

Related questions

Passing Objects By Reference or Value in C#

In C#, I have always thought that non-primitive variables were passed by reference and primitive values passed by value. So when passing to a method any non-primitive object, anything done to the object in the method would effect the object …

Read More
What is the use of "ref" for reference-type variables in C#?

I understand that if I pass a value-type (int, struct, etc.) as a parameter (without the ref keyword), a copy of that variable is passed to the method, but if I use the ref keyword a reference to that variable …

Read More
Passing objects by reference vs value

I just want to check my understanding of C#'s ways of handling things, before I delve too deeply into designing my classes. My current understanding is that: Struct is a value type, meaning it actually contains the data members …

Read More