How can I create an open Delegate from a struct's instance method?

Question

I have a struct with a private method that I\'d like to invoke. Since I plan to do this in a performance critical section, I\'d like to cache a delegate to perform the actio

Answer 1

Interesting problem. From this bug report, it looks like this might be a bug that will be fixed in a future version of .NET: http://connect.microsoft.com/VisualStudio/feedback/details/574959/cannot-create-open-instance-delegate-for-value-types-methods-which-implement-an-interface#details

EDIT: actually, I think this bug report is regarding a different issue, so the behavior you're seeing may not actually be a bug.

From that bug report, I gleaned that there is a work-around if you specify the first argument of your delegate as being passed by reference. Below is a complete working example:

public struct A
{
    private int _Value;

    public int Value
    {
        get { return _Value; }
        set { _Value = value; }
    }

    private int SomeMethod()
    {
        return _Value;
    }
}

delegate int SomeMethodHandler(ref A instance);

class Program
{
    static void Main(string[] args)
    {
        var method = typeof(A).GetMethod("SomeMethod", BindingFlags.Instance | BindingFlags.NonPublic);

        SomeMethodHandler d = (SomeMethodHandler)Delegate.CreateDelegate(typeof(SomeMethodHandler), method);

        A instance = new A();

        instance.Value = 5;

        Console.WriteLine(d(ref instance));
    }
}

EDIT: Jon Skeet's answer here also discusses this issue.