[Mono-list] late linking & dynamic invocation ...

Michael Meeks michael@ximian.com
05 Jul 2002 08:40:18 +0100

Hi Miguel,

On Thu, 2002-07-04 at 21:21, Miguel de Icaza wrote:
>    I am having a bit of trouble understanding what the problem is that
> you are trying to solve in the discussion about delegates.  

	:-) well - there were 2 issues that got rather confused I think.

>    For any "callback" function that you might want to call from your
> code, you will need to have a delegate definition

	I'm relatively resigned to that.

> this is just part of
> the contract of the signature, so implementors can create methods
> conforming to this definition.

	Right [ although this is not really necessary IMHO ].

> > 	a) declare your method - with signature:
> > 
> > 		void myAllocateHandler (Widget     w,
> > 				        Allocation a,
> > 					Object     closure)
> > 		{ ... }
> > 	c) re-type the method signature [ in some mangled form ] in the
> > 	   name of the delegate on connection:
> > 
> > 		object.connect (new FooWidgetAllocationObject 
> > 			(myAllocateHandler));
> You do not retype the signature, instead you use the delegate name:
> 	object += new FooWidgetAllocation (myAllocationHandler)
> So there are two sides of the problem:
> 	* The "definition" side, which consists of a delegate
> 	  declaration.
> 	* The "user" side, which consists of doing the object +=
> 	  new DelegateName (Function).

	Ok - the problem is quite simple. In order to reasonably disambiguate
the 'DelegateName' you need to mangle the types into the delegate name,
in a signal handling system there will be a lot of these, thus:

	new DelegateName (fn) -> new DelegateLongIntShortString 

	Do you now see that I typed the signature twice ? [ ok so it takes a
leap of imagination to see that my_long_int_short_string_method is an
arbitrary name for a method of that signature ].

	The tragedy of this all is that I don't care at all about the type of
the delegate, and the method I pass it to will instantly discard that
information -> a generic 'Delegate' reference so, doing all this
redundant typing seems a total waste.

	In short - I want a way to generically create a Delegate with the right
signature from a method; so that we can then generically invoke it later
[ nicely typed signal emissions ].

	In short, it's the tragedy of this:

	Delegate *del = new DelegateLongIntShortString 

	I want to be able to do:

	Delegate *del = new Delegate (my_long_int_short_string_method);

	or better, have an auto-coercion built into the method signature so
that one doesn't have to type "new" anything :-)

	Does that make it clearer ? it's not a matter of type safety, but
linguistic style it seems to me [ and possibly compiler simplicity as
well ;-].


 mmeeks@gnu.org  <><, Pseudo Engineer, itinerant idiot