[cfe-dev] override support for Objective-C

[Stuart Carnie]

I agree, I think __attribute__ is the most appropriate way, as it can be
made compatible with other compilers using macros, and is not changing the
syntax of Objective-C.

Perhaps I was premature in calling the feature "override", as I want the
attribute to serve as an indicator that somewhere in the class hierarchy
there should be a selector with the same signature, regardless of whether it
is an optional from a protocol or from a superclass.

That is:

@interface MyBase
- (void)someMethodWithInt:(NSInteger)value;
@end

@protocol MyProtocol
@optional
- (void)optionalMethod;
@end

@interface MyDerived : MyBase<MyProtocol>

@end

@implementation MyDerived

- (void)someMethodWith*i*nt:(NSInteger)value
__attribute__((overrideOrImplement)) {
}

- (void)optional*m*ethod  __attribute__((overrideOrImplement)) {
}

@end

I want the compiler to issue a warning for both methods, because they do not
match an existing selector in the class hierarchy.  It could even provide
possible matches, similar to how Clang does searches for unknown types.

I assume that adding a new attribute requires changing Clang, as I couldn't
see how this could be added via a plugin.

Thats much for all the discussion.

Cheers,

Stu

*Stuart Carnie, CTO*
*manomio <http://manomio.com/> | in retro we trust!*


On Mon, Nov 29, 2010 at 10:13 PM, Louis Gerbarg <lgerbarg at gmail.com> wrote:

> If you are only looking at this for a compile time warning (as opposed
> to new runtime hooks and altered code generation) then I don't think
> it is semantically similiar to the existing override attribute, and
> that would be a bad jumping off point. Also, if you want something
> purely for static analysis I don't think a whole extension to the
> language syntax is really appropriate. If I were proposing this, I
> would just add a new attribute, lets call it "implementsObjCProtocol"
> . You could then annotate declarations like this:
>
> - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
> __attribute__((implementsObjCProtocol(UITableViewDataSource)));
>
> or even hide it behind a macro
>
> #define LG_IMPLEMENTS_PROTOCOL(x)
>  __attribute__((implementsObjCProtocol(x)))
>
> - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
> LG_IMPLEMENTS_PROTOCOL(UITableViewDataSource);
>
> You could then just store the attribute data hanging off the AST node,
> and in the static analyzer you could write a simple analysis pass that
> checks for all nodes that have the attribute and make sure the method
> part of the protocol they declare. This is basically how the current
> annotations in Foundation, like NS_REQUIRES_NIL_TERMINATION (though
> that is used during compilation for warning analysis not static
> analysis, but the concept is the same).
>
> Louis
>
> On Mon, Nov 29, 2010 at 10:03 PM, Stuart Carnie <stuart.carnie at gmail.com>
> wrote:
> > This is exactly what I am going for, simply to enhance compile-time and
> > static analysis, when the developer has identified they wished to
> override a
> > particular method.
> > I am definitely not looking to introduce method overloading or scoping as
> > that is far too intrusive.
> > Cheers,
> > Stu
> > Stuart Carnie, CTO
> > manomio | in retro we trust!
> >
> >
> > On Mon, Nov 29, 2010 at 6:27 PM, Alexei Svitkine <
> alexei.svitkine at gmail.com>
> > wrote:
> >>
> >> The benefit of an @Override annotation (for e.g. as implemented in Java)
> >> is for the compiler to warn you if you're not actually overriding
> something
> >> when you think you are. Which could happen if the superclass changed
> since
> >> the time you wrote the code or if you made a typo in the method
> >> name/signature.
> >> This is completely orthogonal to overloading. (Though I don't know
> >> Stuart's actual intention.)
> >> -Alexei
> >>
> >>
> >> On Mon, Nov 29, 2010 at 8:13 PM, Chris Lattner <clattner at apple.com>
> wrote:
> >>>
> >>> On Nov 29, 2010, at 4:09 PM, Stuart Carnie wrote:
> >>>
> >>> Hi all,
> >>> I would like to have a go at hacking a little on Clang when a get a bit
> >>> of spare time, and have found that adding support for override would be
> >>> useful little exercise.  I've seen another post referring to Clang's
> support
> >>> for __attribute__((override)), and seems like I could use this as a
> starting
> >>> point.
> >>> Big Nerd Ranch would like to see an @override keyword, as follows:
> >>>
> >>> @override
> >>> - (NSInteger)numberOfSectionsInTableview:(UITableView *)tv
> >>> { ... }
> >>>
> >>> Hi Stuart,
> >>> Is your  goal here to allow overloading of ObjC methods?  If so, the
> >>> parsing isn't the hard part, you'd need to mangle selectors somehow,
> and
> >>> enhance the runtime to support this.  This isn't something we want in
> ObjC,
> >>> because want to keep it simple.
> >>> -Chris
> >>>
> >>> _______________________________________________
> >>> cfe-dev mailing list
> >>> cfe-dev at cs.uiuc.edu
> >>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >>>
> >>
> >
> >
> > _______________________________________________
> > cfe-dev mailing list
> > cfe-dev at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >
> >
>
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