Passing reference type parameters to a method in C#

Introduction

In developer fraternity, passing of reference type as a parameter to a method is always a topic of hot discussion. The two issues namely (i) passing the parameters (ii) type of parameters are always taken for one another and mostly it is concluded that the passing mechanism doesn’t make any difference to reference type parameters. It seems true to most of developers but actually it’s not complete truth. Let’s see how it works. We all know that by default all parameters are passed by value.

Example:

We have a class named Person (it’s a reference type) as following.

public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public Person(string firstName, string lastName)
{
this.FirstName = firstName;
this.LastName = lastName;
}
}

Console application:

class Program
{
static void Main(string[] args)
{
Person myPerson = new Person("Anand","Rathod"); //instantiate the object
Console.WriteLine(myPerson.FirstName + " " + myPerson.LastName);
PassPersonByVal(myPerson);
Console.WriteLine("After pass by value" + myPerson.FirstName + " " + myPerson.LastName);
PassPersonByRef(ref myPerson);
Console.WriteLine("After pass by ref" + myPerson.FirstName + " " + myPerson.LastName);
Console.ReadLine();
}
 
//method where object is passed by value
static void PassPersonByVal(Person person)
{
//change the properties of person object
person.FirstName = "FirstNameByVal";
person.LastName = "LastNameByVal";
Console.WriteLine(person.FirstName + " " + person.LastName);
person = new Person("NewFirstNameByVal", "NewLastNameByVal");
Console.WriteLine(person.FirstName + " " + person.LastName);
}
 
//method where object is passed by ref
static void PassPersonByRef(ref Person person)
{
//change the properties of person object
person.FirstName = "FirstNameByRef";
person.LastName = "LastNameByRef";
Console.WriteLine(person.FirstName + " " + person.LastName);
person = new Person("NewFirstNameByRef", "NewLastNameByRef");
Console.WriteLine(person.FirstName + " " + person.LastName);
}
}

When a reference type is passed by value to a method then as the parameter is reference to Person object when the passed object is changed the original variable doesn’t get changed. (Refer to above code)

When a reference type is passed by reference and its values are changed then the original value is also changed. (Refer to above code)

Output:

Before calling the methods, FirstName:Anand  LastName:Rathod
In PassPersonByVal() FirstName:FirstNameByVal LastName:LastNameByVal
In PassPersonByVal() FirstName:NewFirstNameByVal LastName:NewLastNameByVal
After calling pass by valueFirstNameByVal  LastName:LastNameByVal
In PassPersonByRef() FirstName:FirstNameByRef  LastName:LastNameByRef
In  PassPersonByRef() FirstName:NewFirstNameByRef LastName:NewLastNameByRef
After calling pass by refFirstName:NewFirstNameByRef  LastName:NewLastNameByRef

Conclusion:

When parameters are passed by ref and such parameters are changed in the method then such changes are applied to original variable passed and such changes persist.

References: