Thank Ben. 2017-04-20 12:49 GMT+04:00 Ben Coman <b...@openinworld.com>:
> Okay that helps a lot. You've done two things wrong. > > 1. You actually did.... > ExternalStructure subclass: #MyStructure > not > FFIExternalStructure subclass: #MyStructure > > This is what caused the error, since if you compare > the class-side methods (by clicking the <Class> button) > of ExternalStructure and FFIExternalStructure > you'll see only the latter has method #rebuildFieldAccessors. > > > 2. You didn't click the <Class> button before adding method #fieldsDesc. > This would trip you up after you fix the above. > "MyStructure rebuildFieldAccessors" would no longer produce an error > but *nothing* would happen when you evaluate it. > When you add #fieldsDesc to the class-side, switch back to the > instance-side > to observe what happens when you evaluate "MyStructure > rebuildFieldAccessors". > > You'll know you are looking at the class-side when you see the class's > class-side definition > MyStructure class > instanceVariableNames: '' > > rather than the class's instance-side definition... > FFIExternalStructure subclass: #MyStructure > instanceVariableNames: '' > classVariableNames: '' > package: 'FFIDemo' > > Pay attention that the documentation says > MyStructure class>>#fieldsDesc > rather than > MyStructure>>#fieldsDesc > > The former is a method on the class-side > and the latter is a method on the instance-side. > > A weak analogy is that you can think of class-side methods > as the methods of MyStructure factory that produces the the Mystructure > objects. > > Actually I can see how "MyStructure class>>#fieldsDesc" can be > ambiguous to newcomers. > Your mind has not yet been conditioned to catch on that detail and and > glosses over it unconsciously thinking "yes, I know MyStructure is a > class. I'm adding a method to it". > This is something that often catches newcomers. I remember getting > caught on it myself. > > Makes me wonder if documentation instead using "MyStructure > classside>>#fieldsDesc" > is more intention revealing, and making the browser button match this > as <Class Side> > would make working with instance/class-side more obvious to newcomers. > > cheers -ben > > On Thu, Apr 20, 2017 at 1:52 PM, Yuriy Babah <babah.yuri...@gmail.com> > wrote: > > > > I have recorded screencast abaut this my operations with Pharo. > > > > https://drive.google.com/open?id=0B_0p5J9SNPlBOHduQlIxdHI0bk0 > > > > But sometimes I'm moved forvard to operations: > > > > MyStructure rebuildFieldAccessors. -> DoIt -> Ok > > > > myStruct := MyStructure externalNew. -> DoIt -> Ok > > > > myStruct := id: 42. -> MessageDoesUnderstood. > > > > I'm doesn't understand in which cases i got to this moment. > > > > I'm associete that with that what i have a several copy's Pharo. > > And somebody affect to other. > > > > 2017-04-19 18:46 GMT+04:00 Ben Coman <b...@openinworld.com>: > >> > >> Hi Yuriy, > >> > >> Hope I can help. I tried your example in build 60463 and its works > fine. So lets break it down. > >> > >> On Wed, Apr 19, 2017 at 8:46 PM, Yuriy Babah <babah.yuri...@gmail.com> > wrote: > >>> > >>> Hello everyone, > >>> > >>> I'm new to Pharo and have tried do example with structure in Unified > FFI manual. > >>> > >>> FFIExternalStructure subclass: #MyStructure > >>> instanceVariableNames: '' > >>> classVariableNames: '' > >>> package: 'FFIDemo' > >> > >> > >> You opened a System Browser and entered and accepted the above first on > its own, > >> such that the new package & class were added and the new class selected. > >> > >> Then you clicked on the <Class> button, such that the "no messages" > text in the third pane changed from > >> normal font to bold font. Then clicked on "no messages" to display the > method template.... > >> messageSelectorAndArgumentNames > >> "comment stating purpose of message" > >> | temporary variable names | > >> statements > >> > >> And replaced that text with the text below from "fieldsDesc" onwards, > >> the Accepted that. > >> > >>> > >>> MyStructure class>>#fieldsDesc > >>> ^ #( > >>> uint8 id; > >>> char * struct_name; > >>> uint name_length; > >>> ) > >>> > >> > >> Then separately you evaluated(doIt) the following... > >> > >>> > >>> MyStructure rebuildFieldAccessors > >> > >> > >> > >>> > >>> . -> DoIt -> MessageNotUnderstood > >>> > >>> What's i do wrong? > >> > >> > >> Does a debug window appear? What is the exact text of the title bar, > >> which details which message is not understood by which class. > >> This provides an important hint to what is wrong. > >> > >> Further help might need a live chat. I'll be in discord for a couple of > hours, but ask anyone there... > >> https://discord.gg/KCKQSSt > >> > >> cheers -ben > >> > >>> I do it in > >>> Pharo5 and 6, widows and os x. > >>> Sorry for my english, it's not my native language. > >>> > >> > >> Your english is not too bad :) > >> > >> cheers -ben > > > > > >
