๐ง 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.
๐ 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
โ
Benefits of var
- Cleaner and more concise code
- Useful with anonymous types and long generic declarations
โ Limitations
- You must assign a value immediately
- Cannot assign
null without a type context
var user = null; // โ Compile-time error: Cannot infer type
โ
Best Use Cases
- LINQ queries
- Anonymous types
- Avoiding repetition
var dictionary = new Dictionary<string, List<int>>();
๐ง 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
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Benefits of object
- Can hold any type
- Enables polymorphic behavior
- Often used in generic data structures
โ Limitations
- Requires explicit casting
- Can introduce boxing/unboxing overhead
object score = 90; int number = (int)score; // Unboxing
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Best Use Cases
- Storing mixed-type data
- Designing APIs that handle various types
๐ฅ 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); // โ Runtime error!
โ
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
โ Limitations
- No compile-time safety
- Slower performance
- Higher risk of runtime exceptions
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Best Use Cases
- Interacting with dynamic data like APIs
- Office Interop, dynamic UI components
- Using
ExpandoObject or reflection
๐ Comparison Table: var vs dynamic vs object
| Feature |
var |
dynamic |
object |
| Type Resolution |
Compile-time |
Runtime |
Compile-time |
| Type Safety |
โ
Yes |
โ No |
โ
Yes (with casting) |
| IntelliSense Support |
โ
Full |
โ Limited |
โ
Full |
| Performance |
โ
High |
โ Lower |
โ Moderate (boxing) |
| Requires Initialization |
โ
Yes |
โ No |
โ No |
| Ideal Use Case |
Known static types |
Flexible runtime |
General base type |
๐งช Practical Examples
โ
var Usage
var city = "New York"; // Inferred as string
var count = 100; // Inferred as int
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object Usage
object data = 42; int result = (int)data; // Requires casting
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dynamic Usage
dynamic user = new { Name = "Alice", Age = 30 }; Console.WriteLine(user.Name); // Works
user = 123; Console.WriteLine(user.Name); // โ Runtime Error
๐ง 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 |
๐ 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.
- โ
Use
var for clarity and compile-time safety.
- โ
Use
object for flexibility with known types and casting.
- โ
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.