C# 4.0 'dynamic' doesn't set ref/out arguments

Question

I'm experimenting with `DynamicObject`. One of the things I try to do is setting the values of `ref`/`out` arguments, as shown in the code below. However, I am not able to have the values of `i` and `j` in `Main()` set properly (even though they are set correctly in `TryInvokeMember()`). Does anyone know how to call a `DynamicObject` object with `ref`/`out` arguments and be able to retrieve the values set inside the method? ``` class Program { static void Main(string[] args) { dynamic proxy = new Proxy(new Target()); int i = 10; int j = 20; proxy.Wrap(ref i, ref j); Console.WriteLine(i + ":" + j); // Print "10:20" while expect "20:10" } } class Proxy : DynamicObject { private readonly Target target; public Proxy(Target target) { this.target = target; } public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { int i = (int) args[0]; int j = (int) args[1]; target.Swap(ref i, ref j); args[0] = i; args[1] = j; result = null; return true; } } class…

Accepted Answer

This looks like it could be a bug - probably in `DynamicObject`. If you add a `Wrap` method to `Proxy` like this:

```
public void Wrap(ref int x, ref int y)
{
    target.Swap(ref x, ref y);
}
```

Then even though this is still called dynamically (i.e. the code in `Main` stays the same) the code works... so at least the general "how does a dynamic object work" layer supports pass-by-reference.

I suspect if this is indeed a bug in the DLR, it may be too late to fix for .NET 4 - but it's worth reporting on Connect anyway so it can be fixed in a service pack. Alternatively, if this is a deliberate restriction/limitation, it should be clearly documented in MSDN (which it isn't at the moment, as far as I can see).

C# 4.0 'dynamic' doesn't set ref/out arguments

Solution

Problem