Skip to main content

How to Resolve Error "CS0529: Inherited interface 'interface1' causes a cycle in the interface hierarchy of 'interface2'" in C#

The Compiler Error CS0529 is a circular dependency error. The message reads: "Inherited interface 'InterfaceA' causes a cycle in the interface hierarchy of 'InterfaceB'".

In C# (and logic in general), definitions cannot be circular. If Interface A inherits from Interface B, Interface B cannot turn around and inherit from Interface A. This creates an infinite loop where the compiler cannot determine the base members of either interface because they are defined in terms of each other. The inheritance tree must be a strict hierarchy, not a loop.

This guide explains how to identify and break these cycles.

Understanding Interface Cycles​

When you declare interface Derived : Base, the compiler copies the contract of Base into Derived.

If you declare:

  1. A : B (A contains B)
  2. B : A (B contains A)

The compiler tries to resolve A. It sees it needs B. To resolve B, it sees it needs A. It enters an infinite loop. C# detects this loop immediately and raises CS0529.

Scenario 1: Direct Self-Inheritance​

The simplest form of this error is an interface trying to inherit from itself. This usually happens due to a typo or a copy-paste error.

Example of error​

// ⛔️ Error CS0529: Inherited interface 'IConfig' causes a cycle 
// in the interface hierarchy of 'IConfig'.
// You cannot define IConfig by saying "It is an IConfig".
public interface IConfig : IConfig
{
    void Load();
}

Solution: Remove the Inheritance​

An interface does not need to inherit from anything to be valid.

// ✅ Correct: No inheritance needed.
public interface IConfig
{
    void Load();
}

Scenario 2: Indirect Circular Inheritance​

This scenario is more common in complex systems. Interface A inherits from B, and later on, someone modifies B to inherit from A, unaware of the existing relationship.

Example of error​

File 1:

// IEntity inherits from IIdentifiable
public interface IEntity : IIdentifiable
{
    void Save();
}

File 2:

// ⛔️ Error CS0529: Inherited interface 'IEntity' causes a cycle...
// Someone tried to make IIdentifiable inherit from IEntity.
// Cycle: IEntity -> IIdentifiable -> IEntity
public interface IIdentifiable : IEntity
{
    int Id { get; }
}

Solution: Linearize the Hierarchy​

You must decide which interface is the Base (the foundation) and which is the Derived (the extension).

If IIdentifiable is the smaller concept (just an ID), it should be the base. IEntity is a larger concept (ID + Save), so it inherits from IIdentifiable.

// 1. The Base Interface (No dependencies)
public interface IIdentifiable
{
    int Id { get; }
}

// 2. The Derived Interface (Depends on Base)
// ✅ Correct: The flow is linear (Top -> Bottom).
public interface IEntity : IIdentifiable
{
    void Save();
}
note

Refactoring Tip: If you find that A needs B and B needs A, your interfaces might be too coupled. Consider merging them into one interface or extracting a third, common base interface C that both A and B inherit from.

Conclusion​

CS0529 prevents infinite definition loops.

  1. Trace the Path: Follow the colon : after the interface names.
  2. Find the Loop: Look for A -> B -> A.
  3. Break the Chain: Remove the inheritance from one side to create a clear "Parent -> Child" relationship.

Table of Contents