c# – 带有构建器模式的“dynamic”关键字隐藏扩展方法

我有一个构建器,它在HttpWebRequest上返回一个HttpWebRequest对象和一个扩展方法.

我的一个构建器方法采用字符串参数.当我将构建器方法传递给字符串时,整个过程都有效,但我传递了一个动态变量,它是一个不再有效的字符串.

似乎应该返回类型HttpWebRequestBuilder的构建器方法现在返回动态.

下面的代码是一个简单的重现它,也可用于here

注意

要使其工作,请注释掉.SetBody(dynamicString)行并取消注释.SetBody(json)行.

public class Program
{
    public static void Main()
    {
        dynamic dynamicString = "{ "test" : "value" }";
        string json = "{ "test" : "value" }";

        string test = new HttpWebRequestBuilder()
            .SetRequestType()
            //.SetBody(json) //uncomment this and it works
            .SetBody(dynamicString) //uncomment this and it breaks
            .Build()
            .ExtensionMethod();

        Console.WriteLine(test);
    }

}

public class HttpWebRequestBuilder
{
    private readonly HttpWebRequest _request;

    public HttpWebRequestBuilder() 
    {
        Uri uri = new Uri("http://www.google.com");
        _request = WebRequest.CreateHttp(uri);
    }

    public HttpWebRequestBuilder SetRequestType() 
    {
        _request.Method = "POST";
        _request.ContentType = "application/json";

        return this;
    }

    public HttpWebRequestBuilder SetBody(string json) 
    {
        byte[] bytes = Encoding.UTF8.GetBytes(json);
        _request.ContentLength = bytes.Length;

        using (Stream writer = _request.GetRequestStream())
        {
            writer.Write(bytes,bytes.Length);
            writer.Flush();
        }

        return this;
    }

    public HttpWebRequest Build() 
    {
        return _request;
    }
}

public static class WebRequestExtensions 
{
    public static string ExtensionMethod(this HttpWebRequest webRequest) 
    {
        return "extension method worked";
    }
}

我猜这是动态对象工作方式的奇怪之处.但任何解释都将非常感激.