为什么我不能在隐式转换中返回接口,但ExpandoObject可以吗？

Question

我有一个DynamicObject,我希望它可以转换为IDictionary,完全相同的方式ExpandoObject.例如,将ExpandoObject强制转换为IDictionary是完全有效的:

dynamic ex = new ExpandoObject ();
ex.Field = "Foobar";
IDictionary<string, object> dict = ex as IDictionary<string, object>;
Console.WriteLine (dict["Field"]);

现在我尝试将它实现到我自己的DynamicObject中:

public class MyDynamicObject : DynamicObject
{
    public Dictionary<string, object> members = new Dictionary<string, object> ();

    public override bool TryGetMember (GetMemberBinder binder, out object result)
    {
        if (members.ContainsKey (binder.Name)) {
            result = members[binder.Name];
            return true;
        }
        else {
            result = null;
            return false;
        }
    }
    public override bool TrySetMember (SetMemberBinder binder, object value)
    {
        this.members.Add (binder.Name, value);
        return true;
    }
    public static implicit operator IDictionary<string, object> (MyDynamicObject mydo) 
    {
        return (IDictionary<string, object>) mydo.members;
    }
}

但是编译器将public static implicit operator IDictionary<string, object>在线路上失败,给出错误:"无法转换为接口类型或从接口类型转换".如果我将隐式运算符更改为Dictionary,我可以将MyDynamicObject强制转换为Dictionary而不会出现任何问题,但不能将IDictionary强制转换为Dictionary.

ExpandoObject如何做到这一点？

Answer 1

ExpandoObject简单地实现IDictionary<string, object>.

如果您想要具有相同的行为,还需要实现此接口并将所有调用委派给您的members字段.

像这样的东西:

public class MyDynamicObject : DynamicObject, IDictionary<string, object>
{
    public Dictionary<string, object> members = new Dictionary<string, object>();

    public IEnumerator<KeyValuePair<string, object>> GetEnumerator()
    {
        return members.GetEnumerator();
    }

    public void Add(KeyValuePair<string, object> item)
    {
        members.Add(item.Key, item.Value);
    }

    // ...
}