Passing reference types to methods in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Passing reference types to methods

Create object in memory

↓

Pass object reference to method

↓

Method receives reference

↓

Modify object properties

↓

Return from method

↓

Original object reflects changes

When you pass a reference type to a method, the method gets a reference to the same object, so changes inside the method affect the original object.

Execution Sample

C Sharp (C#)

class Person {
  public string Name;
}

void ChangeName(Person p) {
  p.Name = "Alice";
}

Person person = new Person();
person.Name = "Bob";
ChangeName(person);

This code creates a Person object with Name 'Bob', passes it to ChangeName, which changes the Name to 'Alice'.

Execution Table

Step	Action	Variable/Parameter	Value Before	Value After	Notes
1	Create Person object	person	null	Person instance with Name=null	Object created in memory
2	Assign Name	person.Name	null	"Bob"	Set initial name to Bob
3	Call ChangeName(person)	p (parameter)	null	Reference to person object	Method receives reference
4	Inside ChangeName: p.Name = "Alice"	p.Name	"Bob"	"Alice"	Name property changed via reference
5	Return from ChangeName	person.Name	"Alice"	"Alice"	Original object reflects change

💡 Method ends; original object's Name is now 'Alice' because reference was passed

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
person.Name	null	"Bob"	"Alice"	"Alice"
p.Name	null	N/A	"Alice"	N/A (parameter scope ends)

Key Moments - 3 Insights

Why does changing p.Name inside the method affect person.Name outside?

Because p is a reference to the same object as person, so modifying p.Name changes the original object's property (see execution_table step 4).

Does the method get a copy of the object or the reference?

The method gets a copy of the reference, not the object itself. Both person and p point to the same object (see execution_table step 3).

What if we assign p = new Person() inside the method?

Assigning p to a new object changes only the local reference p, not the original person variable outside the method.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the value of p.Name after assignment?

A null

B "Bob"

C "Alice"

D Undefined

💡 Hint

Check the 'Value After' column for step 4 in execution_table.

At which step does the original person.Name change to "Alice"?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at when p.Name is assigned "Alice" inside the method in execution_table.

If inside ChangeName we assign p = new Person(), what happens to person.Name outside?

A person.Name remains unchanged

B person.Name changes to new object's Name

C person becomes null

D person.Name becomes null

💡 Hint

Remember that assigning p to new object changes only local reference, original person stays same.

Concept Snapshot

Passing reference types means methods get a reference to the same object.
Changes to object properties inside the method affect the original object.
The method parameter holds a copy of the reference, not a copy of the object.
Assigning the parameter to a new object does not affect the original reference.
Use this to modify objects inside methods easily.

Full Transcript

In C#, when you pass a reference type like an object to a method, the method receives a copy of the reference pointing to the same object in memory. This means if the method changes properties of the object, those changes are visible outside the method. For example, if you have a Person object with a Name property set to 'Bob' and pass it to a method that changes Name to 'Alice', after the method call, the original Person's Name will be 'Alice'. However, if inside the method you assign the parameter to a new object, this does not affect the original object outside. This behavior is because the reference itself is passed by value, but it points to the same object. Understanding this helps you predict how objects behave when passed to methods.