Why does dynamic.ToString () return something between a string and not a string?

Question

I am using a type derived from DynamicObjectas a builder for some strings. In the end, I call ToStringto get the final result.

At that moment, I thought it would give me a normal string, but this string is somehow weird. It behaves like one when I use string functions on it, but it behaves as if I don't know what, that neither a string nor a speaker.

---

This is how I implemented ToStringon my builder

public class Example : DynamicObject
{
    public override bool TryConvert(ConvertBinder binder, out object result)
    {
        if (binder.ReturnType == typeof(string))
        {
            result = ToString();
            return true;
        }
        result = null;
        return false;
    }   

    public override string ToString()
    {
        return base.ToString();
    }
}

When I run it like this

dynamic example = new Example();
Console.WriteLine(example.ToString().ToUpper());

the result is correct: USERQUERY+EXAMPLE(when executed in LINQPad)

However, if I call the second line as follows

Console.WriteLine(example.ToString().Extension());

Where

static class Extensions
{
    public static string Extension(this string str)
    {
        return str.ToUpper();
    }
}

application crashes using RuntimeBinderExceptionspeaking

'string' does not contain a definition for 'Extension'

,

Console.WriteLine(((string)example.ToString()).Extension());

---

, .

Console.WriteLine((string)example); // UserQuery+Example

Console.WriteLine(example); // DynamicObject UserQuery+Example 

, , .

---

, - ?

Answer 1

, ToString, dynamic, dynamic, string:

dynamic example = new Example();
// test will be typed as dynamic
var test = example.ToString();

ToUpper test, string.ToUpper . , .

- , , dynamic . .

Extensions.Extension(example.ToString());

- example.ToString() dynamic, , , Extensions.Extension. . .