Question

I have bit confusion about parameters. When we should have to use reference parameter and when should have to use value type parameters while programming with methods/functions in c# ?

Answer 1

You need to be very clear on the distinction between reference types vs value types, and “by value” parameters vs “by reference” parameters.

I have articles on both topics:

• Reference types and value types
• Parameter passing

The two interact somewhat when using a “by value” parameter which is a reference type: in this case the value which copied by value is the reference itself; you can still modify the object that the reference refers to:

void SomeMethod(StringBuilder x)
{
    x.Append("Modified");
}
...

StringBuilder builder = new StringBuilder();
SomeMethod(builder);
Console.WriteLine(builder.ToString()); // Writes "Modified"

Note that this isn’t the same thing as pass-by-reference semantics… if SomeMethod were changed to include:

x = null;

then that wouldn’t make the builder variable null. However, if you also changed the x parameter to be ref StringBuilder x (and changed the calling code appropriately) then any changes to x (such as setting it to null) would be seen by the caller.

When designing your own API, I would strongly advise you to almost never use ref or out parameters. They can be useful occasionally, but usually they’re an indication that you’re trying to return multiple values from a single method, which is often better done with a type specifically encapsulating those values, or perhaps a Tuple type if you’re using .NET 4. There are exceptions to this rule, of course, but it’s a good starting point.