Var vs Dynamic in C#

Introduction to Var and Dynamic

In C#, both var and dynamic allow for flexibility when declaring variables. However, there are significant differences between the two in terms of how the compiler handles them.

The var keyword is used for implicitly typing local variables. The type is determined by the compiler at compile-time. On the other hand, the dynamic type is resolved at runtime, allowing for more flexibility but at the cost of losing compile-time type safety.

Using Var in C#

The var keyword allows for implicit typing, meaning the compiler determines the type of the variable based on the value it is initialized with. However, the variable remains statically typed, ensuring type safety at compile-time.

Example: Var Keyword

var number = 10;  // The type is inferred as int
var name = "Alice";  // The type is inferred as string

Console.WriteLine(number.GetType());  // Output: System.Int32
Console.WriteLine(name.GetType());  // Output: System.String
        

In this example, var is used for declaring variables. The types are inferred by the compiler at compile-time as int and string.

Using Dynamic in C#

The dynamic keyword is used to declare variables whose type is resolved at runtime. This means the compiler does not perform type checking on dynamic variables, allowing for more flexibility, but also increasing the risk of runtime errors.

Example: Dynamic Keyword

dynamic value = 10;
Console.WriteLine(value.GetType());  // Output: System.Int32

value = "Hello";
Console.WriteLine(value.GetType());  // Output: System.String
        

In this example, dynamic is used to declare a variable. The type is determined at runtime and can change as the program runs.

Differences Between Var and Dynamic

While both var and dynamic offer flexibility, there are key differences between the two:

Key Points to Remember

• Use var when the type is known or can be inferred by the compiler at compile-time.
• Use dynamic when the type is not known until runtime or when working with dynamic data (e.g., COM objects, dynamic data from external sources).
• var is strongly typed, ensuring type safety, while dynamic is more flexible but can lead to runtime errors.