I'm trying to use delegates with Mac OS X's carbon events. When you register an event handler with the system, you can pass an arbitrary 4 bytes, which are passed back to you when the event handler is called.

So, I was hoping to use a delegate. In my handler, I try to do this:

extern (C)
OSStatus
EventHandler(EventHandlerCallRef inHandlerCallRef,
                            EventRef inEvent,
                            void* inUserData)
{
    try
    {
        EventHandlerMethod handleEvent = cast (EventHandlerMethod) inUserData;
        .
        .
        .

However, the compiler complains:

DEventHandler.d:119: error: conversion to non-scalar type requested

Why can't I do this?

TIA,
Rick

Rick Mann wrote:
> I'm trying to use delegates with Mac OS X's carbon events. When you register an event handler with the system, you can pass an arbitrary 4 bytes, which are passed back to you when the event handler is called.
> 
> So, I was hoping to use a delegate. In my handler, I try to do this:
> 
> extern (C)
> OSStatus
> EventHandler(EventHandlerCallRef inHandlerCallRef,
>                             EventRef inEvent,
>                             void* inUserData)
> {
>     try
>     {
>         EventHandlerMethod handleEvent = cast (EventHandlerMethod) inUserData;
>         .
>         .
>         .
> 
> However, the compiler complains:
> 
> DEventHandler.d:119: error: conversion to non-scalar type requested
> 
> Why can't I do this?
> 
> TIA,
> Rick
> 

Delegates are 8 bytes. They consist of a function pointer and a context pointer. I'm not familiar with Carbon's event handling, but I suspect that void* is intended to serve the same purpose as a delegate's context pointer.

-- 
Kirk McDonald
http://kirkmcdonald.blogspot.com
Pyd: Connecting D and Python
http://pyd.dsource.org

Kirk McDonald Wrote:

> Delegates are 8 bytes. They consist of a function pointer and a context pointer. I'm not familiar with Carbon's event handling, but I suspect that void* is intended to serve the same purpose as a delegate's context pointer.

Yeah, I finally figured this out. I thought the delegate was actually a reference to the 8 bytes, in the same way a class type is a reference. I just needed to take the address of the delegate, and it worked fine. Thanks!