Difference Between var, dynamic, and object in C#

🧠 Introduction

If you're new to C# or coming across different types like var, dynamic, and object. It's easy to feel confused. They all seem to allow you to define variables flexibly—but how they work under the hood is very different.

In this article, we'll explore their behavior, performance, type safety, and use cases, with real-world examples to help you master each one.

📌 What is var?

The var keyword enables compile-time type inference. This means the C# compiler determines the type of the variable when you assign it a value.

var age = 30; // Inferred as int var name = "Mahesh"; // Inferred as string

✅ Benefits of var

• Cleaner and more concise code
• Useful with anonymous types and long generic declarations

❌ Limitations

• You must assign a value immediately
• Cannot assign null without a type context

var user = null; // ❌ Compile-time error: Cannot infer type

✅ Best Use Cases

• LINQ queries
• Anonymous types
• Avoiding repetition

var dictionary = new Dictionary<string, List<int>>();

🧊 What is object?

object is the base type from which all .NET types derive—both value types and reference types.

object value = 42;       // Boxed int
object message = "Hello"; // Reference to string

✅ Benefits of object

• Can hold any type
• Enables polymorphic behavior
• Often used in generic data structures

❌ Limitations

• Requires explicit casting
• Can introduce boxing/unboxing overhead

object score = 90; int number = (int)score; // Unboxing

✅ Best Use Cases

• Storing mixed-type data
• Designing APIs that handle various types

🔥 What is dynamic?

Introduced in C# 4.0, the dynamic keyword defers type checking to runtime.

dynamic user = "Mahesh";
Console.WriteLine(user.Length); // OK at runtime

user = 100;
Console.WriteLine(user.Length); // ❌ Runtime error!

✅ Benefits of dynamic

• Great for working with COM objects, JSON, XML, or reflection
• No need to cast or declare types explicitly
• Simplifies dynamic data access

❌ Limitations

• No compile-time safety
• Slower performance
• Higher risk of runtime exceptions

✅ Best Use Cases

• Interacting with dynamic data like APIs
• Office Interop, dynamic UI components
• Using ExpandoObject or reflection

📊 Comparison Table: var vs dynamic vs object

Feature	var	dynamic	object
Type Resolution	Compile-time	Runtime	Compile-time
Type Safety	✅ Yes	❌ No	✅ Yes (with casting)
IntelliSense Support	✅ Full	❌ Limited	✅ Full
Performance	✅ High	❌ Lower	❌ Moderate (boxing)
Requires Initialization	✅ Yes	❌ No	❌ No
Ideal Use Case	Known static types	Flexible runtime	General base type

🧪 Practical Examples

✅ var Usage

var city = "New York"; // Inferred as string 
var count = 100; // Inferred as int

✅ object Usage

object data = 42; int result = (int)data; // Requires casting

✅ dynamic Usage

dynamic user = new { Name = "Alice", Age = 30 }; Console.WriteLine(user.Name); // Works 
user = 123; Console.WriteLine(user.Name); // ❌ Runtime Error

🧠 Summary: Which One Should You Use?

Scenario	Use
You know the type at compile time	var
You want to hold any type with casting	object
You need flexibility at runtime	dynamic
You want maximum performance & safety	var
You're parsing JSON or dynamic data	dynamic

🚀 Final Thoughts

Choosing between var, dynamic, and object isn't just about preference—it's about understanding type behavior, runtime safety, and performance trade-offs.

• ✅ Use var for clarity and compile-time safety.
• ✅ Use object for flexibility with known types and casting.
• ✅ Use dynamic when working with truly dynamic structures or external data, where types aren't known until runtime.

Mastering these three will make your C# code more robust, readable, and maintainable.