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How to Resolve Error "CS0110: The evaluation of the constant value involves a circular definition" in C#

The Compiler Error CS0110 is a logical recursion error that occurs at compile-time. The message reads: "The evaluation of the constant value for 'MyConstant' involves a circular definition".

In C#, a const value is replaced precisely at the places it is used during compilation (similar to "Find and Replace"). To do this, the compiler must be able to calculate the exact value of the constant immediately. If Constant A depends on Constant B, and Constant B depends back on Constant A, the compiler enters an infinite loop and fails with this error.

This guide explains how to identify these cycles and break them using runtime initialization.

Understanding Constant Evaluation​

When you define const int X = 10;, the compiler burns the number 10 into the DLL wherever X is used.

If you define const int X = Y + 1;, the compiler looks for Y. If Y is defined as const int Y = X + 1;, the compiler gets stuck:

  1. To evaluate X, I need Y.
  2. To evaluate Y, I need X.
  3. To evaluate X, I need Y... (Loop detected).

Scenario 1: Direct Self-Reference​

The simplest form of this error is defining a constant in terms of itself.

Example of error​

public class MathConfig
{
    // ⛔️ Error CS0110: The evaluation of the constant value for 'MaxLimit' 
    // involves a circular definition.
    // You cannot use 'MaxLimit' to define 'MaxLimit'.
    public const int MaxLimit = MaxLimit + 10;
}

Solution​

Use literal values or constants that are already fully defined.

public class MathConfig
{
    public const int BaseLimit = 100;
    
    // ✅ Correct: BaseLimit is a known fixed value (100).
    public const int MaxLimit = BaseLimit + 10;
}

Scenario 2: Indirect Circular Dependency​

This scenario is harder to spot because it often spans multiple classes or files. Class A references Class B, which references Class A.

Example of error​

public class ClassA
{
    // Uses ClassB.ValueB to define ValueA
    public const int ValueA = ClassB.ValueB + 1;
}

public class ClassB
{
    // ⛔️ Error CS0110: Uses ClassA.ValueA to define ValueB.
    // This creates a loop: A -> B -> A.
    public const int ValueB = ClassA.ValueA + 1;
}

Solution: Use static readonly instead of const​

If you need values to depend on each other logically, you cannot use const because const requires resolution at compile-time.

Instead, use static readonly. These are evaluated at runtime (specifically, when the class is initialized). This satisfies the compiler because it doesn't need to calculate the final number during the build process.

Solution​

Change const to static readonly.

public class ClassA
{
    // ✅ Correct: The compiler creates a placeholder for this field
    // and calculates the value when the program runs.
    public static readonly int ValueA = ClassB.ValueB + 1;
}

public class ClassB
{
    // ✅ Correct: Runtime evaluation breaks the compile-time loop.
    public static readonly int ValueB = 10; 
}
note

Be Careful: While static readonly fixes the compiler error, circular dependencies can still be tricky at runtime. Depending on which class loads first, one of the values might be initialized to 0 temporarily. It is best to ensure at least one value is a hardcoded literal (the "root" value).

Conclusion​

CS0110 prevents the compiler from freezing in an infinite calculation loop.

  1. Trace the Chain: Look at the constant mentioned in the error. Follow what variables it points to.
  2. Find the Loop: You will eventually find that variable A points to B, and B points back to A.
  3. Break the Chain:
    • Hardcode one of the values to be a literal number/string.
    • Or, switch from const to static readonly to move the calculation to runtime.

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