How to pass references as arguments in a method in c#

Question

How can you pass refernces in C#?

Answer 1

Jon Skeet has a good article on this here.

In C#, value types (like int, double, byte and structs) are passed by value, by default. This means that the receiving method has a NEW instance of the type. If an int that has a value of 1 is passed to the method, and the method changes it to 2, this change is only reflected within the method, the calling location's int is still 1. If however the ref keyword is added, then changes made to that integer are reflected back to the calling location.

All classes in C# are reference types. This means, by default, the references are passed by value. This is the important part. This means, changes made to that instance of the object are reflected back to the calling location, because it is the same object. However, if the method changes it's reference to a different object, this change is not reflected. In the case you want these changes reflected back, you would need to use the ref keyword on the parameter.

    public static void Main()
    {
        int i = 1;
        Method1(i); //i here is still 1
        Method2(ref i); //i is now 2


        SimpleObj obj = new SimpleObj();
        obj.Value = 1;

        Method3(obj); //obj.Value now 2
        Method4(obj); // obj.Value still 2
        Method5(ref obj); //obj.Value now 5
    }

    private static void Method5(ref SimpleObj obj)
    {
        obj = new SimpleObj();
        obj.Value = 5;
    }

    private static void Method4(SimpleObj obj)
    {
        obj = new SimpleObj();
        obj.Value = 5;
    }

    private static void Method3(SimpleObj obj)
    {
        obj.Value++;
    }

    private static void Method2(ref int i)
    {
        i++;
    }

    private static void Method1(int i)
    {
        i++;
    }

    public class SimpleObj
    {
        public int Value { get; set; }
    }

The ref keyword is covered in section 10.6.1.2 of the C# 3.0 specification. Here is the msdn documentation.