On 22 May 2020, at 15:25, Esteban Lorenzano <estebanlm@netc.eu> wrote:
On 22 May 2020, at 15:07, Ben Coman <btc@openinworld.com <mailto:btc@openinworld.com>> wrote:
On Fri, 22 May 2020 at 15:25, Esteban Lorenzano <estebanlm@netc.eu <mailto:estebanlm@netc.eu>> wrote:
On 22 May 2020, at 04:24, Sean P. DeNigris <sean@clipperadams.com <mailto:sean@clipperadams.com>> wrote:
Esteban Lorenzano wrote
The class comments are not clear?
Maybe it's me ;-)
No. I struggled with this also, and still don't have it fully grasped. I could follow Eteban's advice in a particular case I asked about, but still feel hard to reason about next time. http://forum.world.st/typedef-pointerArity-for-FFIOpaqueObjects-td4914975.ht... <http://forum.world.st/typedef-pointerArity-for-FFIOpaqueObjects-td4914975.ht...> http://forum.world.st/UFFI-isPointer-absolute-or-versus-naturalPointerArity-... <http://forum.world.st/UFFI-isPointer-absolute-or-versus-naturalPointerArity-...>
Esteban Lorenzano wrote
Opaque object = https://en.wikipedia.org/wiki/Opaque_data_type <https://en.wikipedia.org/wiki/Opaque_data_type> <https://en.wikipedia.org/wiki/Opaque_data_type> <https://en.wikipedia.org/wiki/Opaque_data_type>>; External object = a pointer to something.
For example, why is ObjCClass a subclass of FFIExternalObject instead of FFIOpaqueObject when the docs say that a "Class [is] An opaque type that represents an Objective-C class"? Also, is the distinction just conceptual? I don't see what either class "buys" you in behavior since they are siblings that both pretty much have no methods.
This is because ObjCClass = SomeOpaqueStructurePointer (is already a pointer), same as ObjCSelector and ObjCMethod. Difference is subtle, because is just a different way of representing the same.
The easiest way I have to explain is:
As a prelude to my next comment, how does "External" distinguish between the two case? Aren't both cases dealing with external C data?
You use an OpaqueObject when you will refer to "the opaque type" in calls as: someFunction(opaqueobject *someArg). You use an ExternalObject when you will refer to "the opaque type" in calls as: someFunction(externalobject someArg).
That makes the distinction really clear. So if now IIUC, both cases deal with "opaque types" with the *only* difference between the two being the arity? Then I propose the following naming would be more intention revealing...
OpaqueObject when you will refer to "the opaque type" in calls as: someFunction(opaqueobject *someArg). OpaquePointer when you will refer to "the opaque type" in calls as: someFunction(opaquepointer someArg).
And to test my new understanding, the matching typdefs and FFI calls would be...
OPAQUE OBJECT - typedef MyOpaqueType opaqueobject. - int someFunction(opaqueobject *someArg)
- FFIOpaqueObject subclass: #MyOpaqueType. - self ffiCall: #(int someFunction( MyOpaqueType *ot ) ). - opaque type has arity 0, so FFI needs to take a pointer to it
OPAQUE POINTER - typedef MyOpaqueObject *opaquepointer. - int someFunction(opaquepointer someArg)
- FFIOpaquePointer subclass: # MyOpaqueType. - self ffiCall: #(int someFunction( MyOpaqueType ot ) ). - opaque type has arity of 1, so FFI uses it directly
The latter FFI call is without the *⦠because FFIOpaquePointer is already a pointer. In practice, both FFI calls are identical, and you use the one that matches the C header definitions.
...or maybe I still don't get it.
No, you got it :) Part of the confusion is the horribly bad name that FFIExternalObject has :/ Other part is my inability to explain it ;)
But yes, this is all as you say. If someone wants to do a PR changing the names and maybe enhancing my comments⦠it would be nice :D Of course keeping the old names as deprecated! ;)
Esteban
cheers -ben