C#:Creating Multicast delegate with boolean return type

Question

Hai Techies,

in C#, how can we define the multicast delegate which accepts a DateTime object and return a boolean.

Thanks

Answer 1

class Test
{
    public delegate bool Sample(DateTime dt);
    static void Main()
    {
        Sample j = A;
        j += B;
        j(DateTime.Now);

    }
    static bool A(DateTime d)
    {
        Console.WriteLine(d);
        return true;
    }
    static bool B(DateTime d)
    {
        Console.WriteLine(d);
        return true;
    }
}

Answer 2

Any delegate can be a multicast delegate

delegate bool myDel(DateTime s);
myDel s = someFunc;
s += someOtherFunc;

msdn

A useful property of delegate objects is that they can be assigned to one delegate instance to be multicast using the + operator. A composed delegate calls the two delegates it was composed from. Only delegates of the same type can be composed.

EDIT: A delagate has a method GetInvocationList which returns a list with the attached methods.

Here is a reference about Delegate invocation

foreach(myDel d in s.GetInvocationList())
{
   d();
}

Answer 3

public delegate bool Foo(DateTime timestamp);

This is how to declare a delegate with the signature you describe. All delegates are potentially multicast, they simply require initialization. Such as:

public bool IsGreaterThanNow(DateTime timestamp)
{
    return DateTime.Now < timestamp;
}

public bool IsLessThanNow(DateTime timestamp)
{
    return DateTime.Now > timestamp;
}

Foo f1 = IsGreaterThanNow;
Foo f2 = IsLessThanNow;
Foo fAll = f1 + f2;

Calling fAll, in this case would call both IsGreaterThanNow() and IsLessThanNow().

What this doesn't do is give you access to each return value. All you get is the last value returned. If you want to retrieve each and every value, you'll have to handle the multicasting manually like so:

foreach(Foo f in fAll.GetInvocationList())
{
    List<bool> returnValues = new List<bool>();
    returnValues.Add(f(timestamp));
}