Const, Static, Readonly in C#

In C#, there are three keywords that are often used to declare constant values: const, static, and readonly. While they may seem similar, each keyword has its own unique features and purposes.

The const keyword is used to declare a constant value that cannot be changed once it has been assigned a value. These values are resolved at compile time and are embedded directly into the intermediate language (IL) code. This means that they are treated as literals and are not associated with any specific instance of a class. For this reason, const values are always static and require a value to be assigned at the time of declaration.

On the other hand, the static keyword is used to declare a member that belongs to the type itself rather than to any specific instance of the type. This means that all instances of the type share the same static member. Static members can be variables, properties, or methods, and they are initialized only once, when the type is first accessed.

Lastly, the readonly keyword is used to declare a constant value that can only be assigned a value during the declaration or within the constructor of the class. This means that a readonly value can be different for different instances of a class, but once it has been initialized, it cannot be changed.

So, when should you use each of these keywords?

Use const when you have a value that will never change and is known at compile time. This could be a mathematical constant like pi or a conversion factor.

Use static when you want to share a variable, property, or method among all instances of a class. For example, a static variable could be used to keep track of the number of instances of a class.

Use readonly when you want a value to be constant for each instance of a class, but can be different across different instances. This could be used for immutable objects or for values that are determined at runtime.

In conclusion, const, static, and readonly are all important keywords in C# that serve different purposes. Understanding when and how to use each of these keywords can help you write more efficient and maintainable code in your C# applications.

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