Question

What does the syntax &function_name mean?

For example, as used in the delegate

System::ComponentModel::DoWorkEventHandler(this, &Form1::DoWorkEvent)

as used with event handling with a BackgroundWorker object.

The delegate prototype is

public delegate void DoWorkEventHandler(Object^ sender, DoWorkEventArgs^ e)

Presumably this means that &Form1::DoWorkEvent returns a DoWorkEventArgs object? But that doesn’t make much sense.

Answer 1

System::ComponentModel::DoWorkEventHandler(this, &Form1::DoWorkEvent) creates a delegate. The syntax for creating a delegate is gcnew delegatename(thisObject, functionPointer). It creates a delegate that calls functionPointer with this set to thisObject.

To invoke a delegate, you call it with the appropriate parameters. delegateVariable->Invoke(parameter1, parameter2, etc). In the case of DoWorkEventHandler, parameter1 is sender and parameter2 is e.

You’re confusing two different things, creation and invocation. The line DoWorkEventHandler(this, &Form1::DoWorkEvent) creates a delegate. The two parameters are thisObject and functionPointer, not sender and e.

This should have been covered by whatever book/resource you used to learn about delegates in the first place. For example, this article says

Creating a delegate instance involves calling a constructor. If you
are encapsulating a static function, you pass in one argument, a
pointer to that member function. For an instance function, you must
pass in two arguments: a handle to that instance, as well a pointer to
the instance member function.