CODEWITHSUNDEEP
c#c#-4.0inheritancedynamicinterface
Stuart Golodetz
Stuart Golodetz

Reputation: 20626

Why does dynamic binding fail when using interface inheritance?

In C#, please does anyone know why I can't do the following? (specifically the line marked 'NOT fine!' below)

interface A
{
    void Add(dynamic entity);
}

interface B : A {}

class C : B
{
    public void Add(dynamic entity)
    {
        System.Console.WriteLine(entity);
    }
}

class Program
{
    static void Main(string[] args)
    {
        B b = new C();
        dynamic x = 23;
        b.Add(23);        // fine
        b.Add((int)x);    // fine
        (b as A).Add(x);  // fine
        //b.Add(x);       // NOT fine!
    }
}

I have absolutely no problems if the call isn't dynamically-bound, or if I explicitly cast to the interface at the root of the hierarchy, but the dynamically-bound call gives me:

Unhandled Exception: Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: No overload for method 'Add' takes '1' arguments
   at CallSite.Target(Closure , CallSite , B , Object )
   at System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid2[T0,T1](CallSite site, T0 arg0, T1 arg1)
   at Program.Main(String[] args) in C:\Users\Stuart\Documents\Visual Studio 2010\Projects\CSharp Testbed\Program.cs:line 218

Upvotes: 25

Views: 1580

Answers (2)

Luke Forder
Luke Forder

Reputation: 1189

Looking on Microsoft Connect it's filed as a bug - Dynamic runtime fails to find method from a base interface during runtime

Upvotes: 12

Brad Rem
Brad Rem

Reputation: 6026

It looks like the multiple layers of interface inheritance are doing in the passing of a dynamic type variable. It's definitely tripping up the run time binding.

At this point if you're looking to get it to work a possible workaround is:

dynamic x = 23;
b.Add((object)x);

dynamic y = "Hello, World!";
b.Add((object)y);

Since dynamic is seen as object by the IL, so casting everything explicitly to type object will get this to work for you.

Upvotes: 0

Related Questions