Re: Properties and objc1

[Bertrand Dekoninck]

Le 17/08/2018 à 15:58, Ivan Vučica a écrit :
> Hey,
>
> just some random thoughts regarding what I'd ask of a contributor to a
> project I'd be writing.
>
> This is in addition to David's comment: I would *expect* @property and
> @synthesize to work to the extent you need them to even without
> runtime support. David can correct me, but situation, I believe,
> changes only if you want to query the runtime for which *properties*
> exist and with which attributes, instead of just querying which
> methods exist. I believe this means GNUstep's implementation of Core
> Animation APIs can't be fully featured without libobjc2, because it
> can't construct @dynamic properties without knowing that a property is
> @dynamic. Of course, I need to finish the @dynamic support :-)
>
> I hope what follows helps a bit.
It helps me to understand more things. Thanks.

> On Fri, Aug 17, 2018 at 11:09 AM Bertrand Dekoninck
> <bertrand.dekoninck@gmail.com> wrote:
> > Hi everyone on the list.
> >
> > I'm enjoying my summertime to do some gnustep stuff. I want to convert
> > the rik.theme to objc1 because I can't have libobjc2 running on my ppc
> > computers.
> >
> > For now, I'm dealing with properties.
> >
> > I've managed to convert this one :
> >
> > @property (retain) NSButtonCell * defaultbuttoncell;
> >
> > into :
> >
> > - (NSButtonCell *) defautbuttoncell {
> >     return defaultbuttoncell;
> > }
> >
> > - (void) setdefaultbuttoncell: (NSButtonCell *) defaultbuttoncell_ {
> That should be "setDefaultbuttoncell". (This shows why it's a good
> idea to camelcase your variables; "defaultButtonCell" would result in
> "setDefaultButtonCell:". Assuming you can do that in the theme!)
I did notice that by myself  : I would have named the variable 
defaultButtonCell if it wasnt already named as is. That's why I named 
the setter  setdefaultbuttoncell and didn't think to your solution.
> Naming this correctly helps KVC/KVO work correctly. I *think* you *do
> not* need to notify KVO of the change in value. If it turns out you
> do, just call "willChangeValueForKey:" and "didChangeValueForKey:"
> (iirc) manually.
 KVC/KVO ? I don't know anything about this. I should dig a little. In 
fact, yesterday, I didn't know what properties were doing and I'm 
leveling my skills a little up now. So you can understand this part of 
your comment is completely obscure to me. Don't matter.
> >     [defaultbuttoncell_ retain];
> >     [defaultbuttoncell release];
> >     defaultbuttoncell = defaultbuttoncell_;
> > }
>
> (1)
> I like to use "self->" to make it clear that I'm referring to an ivar.
> So [defaultbuttoncell_ retain]; [self->defaultbuttoncell release];
> self->defaultbuttoncell = defaultbuttoncell_;.
>
> (2)
> Tendency for the past few years seems to be to use ivars named
> "_propertyname". (While @synthesize will default to naming the ivar
> the same, so "propertyname", if you omit @synthesize and the ivar
> completely on modern Clang, it'll use "_propertyname" by default.)
> So:
> {
>    NSButtonCell * _defaultbuttoncell;
> }
> @property (retain) NSButtonCell * defaultbuttoncell;
> ...
> @synthesize defaultbuttoncell=_defaultbuttoncell;
I found explanations about properties at 
https://www.quora.com/How-are-atomic-properties-implemented-in-ObjC?share=1 
and I followed the notation.

> (3) Finally I'd add a small check:
>    if (self->defaultbuttoncell == defaultbuttoncell_)
>      return;
What for ? To escape without the 3 lines that follow if true ?

> So this is what it'd look like (assuming you can apply all these in a theme):
>
> @interface Whatever
> {
>    NSButtonCell * _defaultButtonCell;
> }
> - (NSButtonCell *) defaultButtonCell;
> - (void) setDefaultButtonCell: (NSButtonCell *) defaultButtonCell;
> @end
>
> @implementation Whatever
> - (NSButtonCell *) defaultButtonCell
> {
>    return self->_defaultButtonCell;
> }
>
> - (void) setDefaultButtonCell: (NSButtonCell *) defaultButtonCell
> {
>    if (defaultButtonCell == self->_defaultButtonCell)
>      return;
>
>    [defaultButtonCell retain];
>    [self->_defaultButtonCell release];
>    self->_defaultButtonCell = defaultButtonCell;
> }
> @end
>
> This seems clear and readable to me, if you are attempting to avoid
> @synthesize. But, I might be embarrassing myself by missing something
> obvious.
I've read a little more on atomic/non atomic attributes and was 
wondering if atomic is anything useful for a theme : should it be 
threadsafe ? If so, should I use @synchronize ? and would it be 
available without libobjc2 and libdispatch ?

Anyway, the whole discussion is now useless if gcc supports properties.

> > And I  want to be sure for this one because of the non atomic and assign
> > attributes :
> >
> > @property (nonatomic, assign) BOOL reverse;
> >
> > is replaced by :
> >
> > - (BOOL) reverse {
> >     return reverse;
> > }
> > - (void) setReverse: (Bool) reverse_ {
> >     reverse = reverse_;
> >     }
>
> This seems ok, except:
> (1) s/Bool/BOOL/
> (2) I'd still name the ivar "_reverse", the argument "reverse", and
> use "self->" to make it clear I refer to the ivar.

Thanks a lot for this review.

Bertrand