Re: Converting function pointers to delegates
On 4/15/14, Artur Skawina wrote:
> He obviously meant that you can't get a pointer to the object, that the
> reference points to, just by casting and w/o address-of.
Ah right. I don't do this often so I forgot. The proper code would be:
int* f(ref int r) { return &r; }
Re: Converting function pointers to delegates
On Tuesday, 15 April 2014 at 12:05:09 UTC, Artur Skawina wrote: He obviously meant that you can't get a pointer to the object, that the> reference points to, just by casting and w/o address-of. Yea, you can cast a class reference to void* (which does include this inside a class), but not a ref storage class thingy which includes this inside a struct. Since the topic at hand was a struct I got a bit sloppy in my wording. So I'd say we're all partially right, just in different contexts :)
Re: Converting function pointers to delegates
On 04/15/14 13:30, Andrej Mitrovic wrote:
> On 4/15/14, Artur Skawina wrote:
>> It *is* true. Classes are /reference types/, not references to classes.
>
> I meant the part where he said you can't cast a reference to a pointer. You
> can.
He obviously meant that you can't get a pointer to the object, that the
reference points to, just by casting and w/o address-of.
int* f(ref int r) { return cast(int*)r; }
void main() {
int a = 42;
import std.stdio;
writeln(&a);
writeln(f(a));
}
Yes, this will compile, and, yes, you can "cast a reference to a pointer",
but this does not mean that you will get a pointer to 'a'.
The D situation wrt to refs and classes is bad enough; saying that you
"can cast a reference to a pointer" will only confuse people.
artur
Re: Converting function pointers to delegates
On 4/15/14, Artur Skawina wrote: > It *is* true. Classes are /reference types/, not references to classes. I meant the part where he said you can't cast a reference to a pointer. You can.
Re: Converting function pointers to delegates
On 04/14/14 19:51, Andrej Mitrovic wrote: > On Monday, 14 April 2014 at 17:48:31 UTC, Adam D. Ruppe wrote: >> On Monday, 14 April 2014 at 17:45:52 UTC, Ryan Voots wrote: >>> src/yage/core/misc.d(164): Error: e2ir: cannot cast this of type S to type >>> void* >> >> >> Try taking the address of this before casting it. So more like >> >> cast(void*)&this >> >> >> IIRC in D1 this was a pointer, whereas in D2 this is a reference. You can't >> cast a reference to pointer directly. > > That's not true. > > And I think the issue in his diagnostic is that he used it with a struct. You > can't cast 'this' of a struct to a pointer (you'd have to use &this), but you > can cast a class reference to a pointer. It *is* true. Classes are /reference types/, not references to classes. [There's no such thing as a "class payload" in D. Also, you can have a D-ref to a D-class.] D doesn't have "true" references, just a storage-class based hack, that only supports a small subset of ref functionality. But these pseudo-refs still act as the objects they point to. artur
Re: Converting function pointers to delegates
On Monday, 14 April 2014 at 17:45:52 UTC, Ryan Voots wrote: /** * Convert any function pointer to a delegate. * _ From: http://www.digitalmars.com/d/archives/digitalmars You can replaced it with std.functional.toDelegate. As for its use-case, if some API or function supports only delegates but you want to pass in a function, you would wrap the function with toDelegate and then pass the delegate to the API/function.
Converting function pointers to delegates
I'm porting some code from D1 to D2 and this is the final error
i'm getting from DMD and GDC. I have no idea what is going on
with it though.
/**
* Convert any function pointer to a delegate.
* _ From:
http://www.digitalmars.com/d/archives/digitalmars/D/easily_convert_any_method_function_to_a_delegate_55827.html
*/
R delegate(P) toDelegate(R, P...)(R function(P) fp)
{ struct S
{ R Go(P p) // P is the function args.
{ return (cast(R function(P))(cast(void*)this))(p);
}
}
return &(cast(S*)(cast(void*)fp)).Go;
}
DMD tells me:
src/yage/core/misc.d(164): Error: e2ir: cannot cast this of type
S to type void*
The code itself you can see at:
https://bitbucket.org/simcop2387/yage/src/0542cea5eefabf4c90b822cf26ec1062ed0fcb64/src/yage/core/misc.d?at=default#cl-161
and where it gets called:
https://bitbucket.org/simcop2387/yage/src/0542cea5eefabf4c90b822cf26ec1062ed0fcb64/src/yage/core/repeater.d?at=default#cl-47
To be perfectly honest I'm not sure what it's doing to figure out
how to fix it.
Re: Converting function pointers to delegates
On Monday, 14 April 2014 at 17:48:31 UTC, Adam D. Ruppe wrote: On Monday, 14 April 2014 at 17:45:52 UTC, Ryan Voots wrote: src/yage/core/misc.d(164): Error: e2ir: cannot cast this of type S to type void* Try taking the address of this before casting it. So more like cast(void*)&this IIRC in D1 this was a pointer, whereas in D2 this is a reference. You can't cast a reference to pointer directly. That's not true. And I think the issue in his diagnostic is that he used it with a struct. You can't cast 'this' of a struct to a pointer (you'd have to use &this), but you can cast a class reference to a pointer.
Re: Converting function pointers to delegates
On Monday, 14 April 2014 at 17:45:52 UTC, Ryan Voots wrote: src/yage/core/misc.d(164): Error: e2ir: cannot cast this of type S to type void* Try taking the address of this before casting it. So more like cast(void*)&this IIRC in D1 this was a pointer, whereas in D2 this is a reference. You can't cast a reference to pointer directly (at least not without overloading the cast operator) but you can take its address to fetch a pointer out of it and then work with that. BTW see also: http://dlang.org/phobos/std_functional.html#toDelegate
