Question

Let say, I have a MulticastDelegate that implements generic delegate and contains several calls:

Func<int> func = null;
func += ( )=> return 8;
func += () => return 16;
func += () => return 32;

Now this code will return 32:

int x = func(); // x=32

I would like to know if there exists (or better I should ask why it doesn’t exist!) the C# language feature using which is possible to get the access to results of all delegate’s invocations, that means to get the list ({8,16,32})?

Of course it’s possible to do the same using .NET framework routines. Something like this will do the work:

public static List<TOut> InvokeToList<TOut>(this Func<TOut> func)
{
    var returnValue = new List<TOut>();
    if (func != null)
    {
        var invocations = func.GetInvocationList();
        returnValue.AddRange(invocations.Select(@delegate => ((Func<TOut>) @delegate)()));
    }
    return returnValue;
}

But I can’t get out from the system that there should be the better way, at least without casting (really, why MulticastDelegate is not generic when delegates are)?

Answer 1

You can accomplish what you want if you don’t use a Func<int>, but an Action which takes a method as parameter which processes the return values. Here is a small example:

    static Action<Action<int>> OnMyEvent=null;

    static void Main(string[] args)
    {
        OnMyEvent += processResult => processResult(8);
        OnMyEvent += processResult => processResult(16);
        OnMyEvent += processResult => processResult(32);

        var results = new List<int>();
        OnMyEvent(val => results.Add(val));

        foreach (var v in results)
            Console.WriteLine(v);

    }