When Should I Declare a Private Class as Static in C#?

Question

What are the benefits of declaring a private class as static in C# and when should I choose one over the other?

private static class Foo
{
    // Static class members and methods
}

private class Foo
{
    // Instance class members and methods
}

Answer

In C#, the decision to declare a private class as static depends on your design requirements and performance considerations. Choosing between a static and a non-static private class can significantly impact memory usage, accessibility, and lifecycle management.

private static class Utility
{
    public static int Add(int a, int b)
    {
        return a + b;
    }
}

private class InstanceExample
{
    private int instanceVariable;
    public InstanceExample(int value)
    {
        instanceVariable = value;
    }
}

Causes

  • Static classes cannot be instantiated, meaning you cannot create objects from them.
  • Static members belong to the class itself rather than to any specific object, which can save memory when you don't need object-level data.
  • If a class is only intended to contain utility methods or constants, declaring it as static can enforce that design.

Solutions

  • Use a **private static class** when you need a class that should only contain static members or utility methods that belong to the class, not to any instance.
  • Opt for a **private class** when the class requires instance members or methods, or needs to maintain state between method calls.

Common Mistakes

Mistake: Using instance members in a static class.

Solution: Remember that static classes cannot have instance members. Make sure that all members and methods in a static class are static.

Mistake: Declaring a class as static when it needs state management.

Solution: Use a regular private class if you need to maintain state through instance variables.

Helpers

  • private class
  • static class
  • C# programming
  • when to use static class
  • private static class C#

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