C#8.0 中开启默认接口实现方法

<Project Sdk="Microsoft.NET.Sdk">

 <PropertyGroup>
  <OutputType>Exe</OutputType>
  <TargetFramework>netcoreapp3.0</TargetFramework>
  <LangVersion>8.0</LangVersion>
 </PropertyGroup>

</Project>

public interface IWalterlv
{
  void Print(string text);
}

  public interface IWalterlv
  {
    void Print(string text);

++   void DouBPrint(string text);
  }

  public interface IWalterlv
  {
    void Print(string text);
    
--   void DouBPrint(string text);
++   public void DouBPrint(string text) => Print($"Walterlv 逗比 {text}");
  }

class Program
{
  static void Main(string[] args)
  {
    IWalterlv walterlv = new Foo();
    walterlv.DouBPrint("walterlv");
  }
}

public class Foo : IWalterlv
{
  public void Print(string text)
  {
  }
}

public class Foo : IWalterlv
{
  public void Print(string text)
  {
  }

  public void DouBPrint(string text) => Print($"Walterlv 逗比 {text}");
}

 public interface IWalterlv
  {
    void Print(string text);

--   public void DouBPrint(string text) => Print($"Walterlv 逗比 {text}");
++   public void DouBPrint(string text) => DefaultDouBPrint(this, text);
++
++   private static readonly string _name = "walterlv";
++
++   protected static void DefaultDouBPrint(IWalterlv walterlv, string text)
++     => walterlv.Print($"{_name} 逗比 {text}");
  }

  public class Foo : IWalterlv
  {
    public void Print(string text)
    {
    }

--   public void DouBPrint(string text) => Print($"Walterlv 逗比 {text}");
++   public void DouBPrint(string text)
++   {
++     // Do Other things.
++     IWalterlv.DefaultDouBPrint(this, text);
++   }
++ }