Is it possible to declare the implementation of a method directly in the interface definition?

Starting from C# 8.0, interfaces gained the ability to declare method implementations directly within their definitions — this is called "default interface methods." This allows adding new methods to interfaces without breaking existing implementations.

Example:

public interface ILogger
{
    void Log(string message); // regular interface method

    void LogWarning(string message) // default implementation method
    {
        Log("Warning: " + message);
    }
}

Previously, interfaces could only declare method signatures without bodies. Now, methods can have bodies, expanding the capabilities of interfaces.