> On 22 May 2020, at 15:25, Esteban Lorenzano <esteba...@netc.eu> wrote: > > >> On 22 May 2020, at 15:07, Ben Coman <b...@openinworld.com >> <mailto:b...@openinworld.com>> wrote: >> >> >> >> On Fri, 22 May 2020 at 15:25, Esteban Lorenzano <esteba...@netc.eu >> <mailto:esteba...@netc.eu>> wrote: >>> On 22 May 2020, at 04:24, Sean P. DeNigris <s...@clipperadams.com >>> <mailto:s...@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.html >> >> <http://forum.world.st/typedef-pointerArity-for-FFIOpaqueObjects-td4914975.html> >> >> http://forum.world.st/UFFI-isPointer-absolute-or-versus-naturalPointerArity-td4917236.html >> >> <http://forum.world.st/UFFI-isPointer-absolute-or-versus-naturalPointerArity-td4917236.html> >> >> >>> >>> >>> 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 >
