pass a delegate to an API as a context pointer?

[teo]

teo Wrote:

> Hi *, is it possible to pass a delegate to an API function which takes a pointer to a callback function and a context pointer? The code bellow describes what I'm trying to achieve.
> 
<snip>

I got it! Thanks to all of you Russell, Kirk, Jascha and Frits!

Let me summarize: the idea is to keep the delegate in a member variable of the class and pass the address of that variable as a context data. This way the address remains valid when the callback is called from within the C-library.

Perhaps it can be done in a more elegant way, but I'm satisfied with this solution:

// C-Library
typedef void (*callback)(void *context);
void xyz(callback handler, void *context);

// D-Program
alias extern(C) void function(void *context) callback;
extern(C) void xyz(callback handler, void *context);
alias int delegate() foo;

class A
{
	int abc() { return 1; }
}
class B
{
	foo _f = null;
	static extern(C) void handler(void *context)
	{
		foo f = *(cast(foo*)context);
		int i = f(); // call A.abc();
	}
	void test(foo f)
	{
		_f = f; // this way the address remains valid
		xyz(&handler, &_f);
	}
}
void main()
{
	A a = new A();
	B b = new B();
	b.test(&a.abc);
	// ...
	return;
}

By the way, I'm going to play with garbage collector, so I might have further questions.