Virtual method dispatch mechanism in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Virtual method dispatch mechanism

Create base class object

↓

Call virtual method

↓

Check actual object type

↓

If base type

→Call base method

↓

If derived type

→Call overridden method

↓

Return method result

When calling a virtual method, the program checks the actual object's type at runtime and calls the correct method version.

Execution Sample

C Sharp (C#)

class Animal {
  public virtual string Speak() => "Animal sound";
}
class Dog : Animal {
  public override string Speak() => "Bark";
}
Animal a = new Dog();
Console.WriteLine(a.Speak());

This code creates a Dog object but stores it as an Animal reference, then calls Speak(), which runs Dog's version.

Execution Table

Step	Action	Object Type	Method Called	Output
1	Create Dog object assigned to Animal reference	Dog	N/A	N/A
2	Call Speak() on Animal reference	Dog	Dog.Speak()	"Bark"
3	Print output	Dog	N/A	Bark
4	End of execution	N/A	N/A	N/A

💡 Execution stops after printing the overridden method output.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
a	null	Dog object reference	Dog object reference	Dog object reference

Key Moments - 2 Insights

Why does calling Speak() on an Animal reference run Dog's Speak()?

Because the method is virtual, the program checks the actual object type (Dog) at runtime and calls the overridden method (Dog.Speak()), as shown in execution_table step 2.

What if Speak() was not virtual, which method would run?

If Speak() was not virtual, the method called would be based on the reference type (Animal), so Animal.Speak() would run, not Dog.Speak(). This is different from the virtual dispatch shown in step 2.

Visual Quiz - 3 Questions

Look at the execution_table, what method is called at step 2?

A Dog.Speak()

B Animal.Speak()

C Object.ToString()

D Base class constructor

💡 Hint

Check the 'Method Called' column in execution_table row for step 2.

At which step is the Dog object created and assigned?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for object creation.

If Speak() was not virtual, what would be the output at step 3?

A "Bark"

B Compilation error

C "Animal sound"

D No output

💡 Hint

Refer to key_moments explanation about non-virtual method calls.

Concept Snapshot

Virtual method dispatch means calling a method on a base class reference runs the overridden method in the actual object's class.
Use 'virtual' keyword in base class and 'override' in derived class.
At runtime, the program checks the real object type to decide which method to run.
This enables flexible and dynamic behavior in object-oriented programming.

Full Transcript

This example shows how virtual method dispatch works in C#. We create a Dog object but store it in an Animal variable. When we call Speak() on the Animal variable, the program checks the actual object type at runtime, which is Dog, and calls Dog's Speak() method. This is because Speak() is marked virtual in Animal and overridden in Dog. The execution table shows each step: creating the Dog object, calling Speak(), and printing the output. Key moments explain why the overridden method runs and what would happen if the method was not virtual. The visual quiz tests understanding of method calls and object creation steps. Virtual dispatch allows programs to decide which method to run based on the real object, not just the reference type.