Is it possible to define specific implementations of methods within an interface?

In C# starting from version 8.0, it became possible to define method implementations within an interface — these are called default interface methods.

This allows adding new methods to interfaces without breaking existing implementations.

Example:

public interface ILogger
{
    void Log(string message);

    void LogError(string message)  // default interface method
    {
        Log("ERROR: " + message);
    }
}

public class ConsoleLogger : ILogger
{
    public void Log(string message)
    {
        Console.WriteLine(message);
    }
}

Thus, the ConsoleLogger class may not implement LogError, and it will still work by default.