Question

Why doesn’t the C# compiler tell me that this piece of code is invalid?

class Program
{
    static void Main(string[] args)
    {
        dynamic d = 1;
        MyMethod(d);
    }

    public void MyMethod(int i) 
    {
        Console.WriteLine("int");
    }
}

The call to MyMethod fails at runtime because I am trying to call a non-static method from a static method. That is very reasonable, but why doesn’t the compiler consider this an error at compile time?

The following will not compile

class Program
{
    static void Main(string[] args)
    {
        dynamic d = 1;
        MyMethod(d);
    }
}

so despite the dynamic dispatch, the compiler does check that MyMethod exists. Why doesn’t it verify the “staticness”?

Answer 1

Overload resolution is dynamic here. Visible in this code snippet:

class Program {
    public static void Main() {
        dynamic d = 1.0;
        MyMethod(d);
    }

    public void MyMethod(int i) {
        Console.WriteLine("int");
    }

    public static void MyMethod(double d) {
        Console.WriteLine("double");
    }
}

Works fine. Now assign 1 to d and note the runtime failure. The compiler cannot reasonably emulate dynamic overload resolution at compile time, so it doesn’t try.