C# 8.0 默认接口实现基本语法/显式调用

我一直在搞乱默认的接口实现。认为您必须向下转换为接口类型才能使用默认方法实现。我还发现了一堆关于另一种语法的注释，我找不到这是否已经包含在内，我确实找到了关于它的外观的“决定”，但是它不起作用。我做错了吗？还是这个新语法尚未包含在内？

有些相关但没有回答我的问题：从实现结构中调用 C# 接口默认方法而不进行装箱 https://stackoverflow.com/questions/57827493/calling-c-sharp-interface-default-method-from-implementing-struct-without-boxing

注释base<>/base()句法：https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-11-14.md#default-interface-implementations https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-11-14.md#default-interface-implementations

微软关于该提案的页面：https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/default-interface-methods https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/default-interface-methods

class D : IA, IB, IC
{
                  //Notice the use of base() right here.
    void IA.M() { base(IB).M(); }
}

假设我们需要对某个对象进行 INotifyPropertyChanged。我们现在可以在接口上默认实现 SetField ：

public interface INotify : INotifyPropertyChanged
{
    void InvokePropertyChanged(string propertyName);

    bool SetField<T>(ref T field, T value, [CallerMemberName] string propertyName = null)
    {
        INotify thing = (INotify)this;

        if (propertyName == null)
        {
            throw new ArgumentException($"{nameof(propertyName)} is null. PropertyChangedEventHandler will not be fired correctly.");
        }

        if (EqualityComparer<T>.Default.Equals(field, value)) return false;
        field = value;
        InvokePropertyChanged(propertyName);
        return true;
    }
}

实现它需要沮丧（((INotify)this).SetField）， 使用base(INotify)会优先选择这里。

public class Thing : INotify
{
    public string A
    {
        get => _a;
        //Need an explicit cast here. Can't figure out how to use base syntax.
        set => ((INotify)this).SetField(ref _a, value);
    }
    private string _a;

    public event PropertyChangedEventHandler PropertyChanged;

    public void InvokePropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}