On 2013-06-10 08:04:43 +0000, Jacob Carlborg <d...@me.com> said:
On 2013-06-10 09:23, Manu wrote:
That seems pretty awkward to me. Basically a hack.
A function pointer is not a delegate, so I don't see why that should be
used to describe one.
It depends on how you look at it. In D a delegate is a function pointer
with a context pointer. In C++ a pointer to a member function is
basically the same, the context pointer is just passed separately.
But a true member function pointer is also parametrized on the type of
this, unlike a delegate, letting you change the object pointer in a
type-safe manner.
(And implementation-wise, C++ function pointers can be really
complicated beasts in order to support virtual calling and
multiple/virtual inheritance. sizeof can even change depending on the
type of "this". That's not what you want in D.)
I haven't needed to yet... but that doesn't mean it might not be useful.
It would probably be used in D for tight binding with other systems.
AngelScript binds to native code with member function pointers... just
off the top of my head.
Actually I don't see why you can't use a delegate for this. The only
difference is that it won't be virtual.
Type-safety. I mean, you can do this if you want:
auto funcptr = &Object.toString;
auto object = new Object;
// now call our function using object
string delegate() deleg;
deleg.ptr = cast(void*)object;
deleg.funcptr = funcptr;
but this is not type-safe: the funcptr type ("string function()") is
actually wrong (it'll only work if called from a delegate) and the
object pointer the in the delegate is a void*. All Manu is asking is
that funcptr is of a correct type so you can call it directly by
supplying "this" as an argument, like this:
funcptr(object);
The problem is that this "correct type" for the function pointer does
not exist currently. Calling a member function uses a different ABI, so
the type needs to know somehow its a pointer to a member function (and
that its first parameter is "this"), otherwise the generated code at
the call site will be all wrong.
--
Michel Fortin
michel.for...@michelf.ca
http://michelf.ca/
