Macro in Obj-C libraries

Elements C#
1

Some Obj-C libraries expose API by macro (e.g. ReactiveCocoa / extobjc):

 RAC(self, loggedIn) = [[NSNotificationCenter.defaultCenter
    rac_addObserverForName:UserDidLogOutNotification object:nil]
    mapReplace:@NO];

In this code snippet, RAC is a macro defined by ReactiveCocoa which use other macros:

#define RAC(TARGET, ...) \
metamacro_if_eq(1, metamacro_argcount(__VA_ARGS__)) \
    (RAC_(TARGET, __VA_ARGS__, nil)) \
    (RAC_(TARGET, __VA_ARGS__))

It’s unpractical to manually expand the macro for every API call.
As this issue also apply to Oxygen and I wonder what might be the best solution? ( Use cpp pre-processor or maybe writing custom Cirrus Aspect? )

Thanks.

2

Can you show the full thing? I need to see what it really does before I can recommend a workaround.

3

Hi Carlo,
The library is ReactiveCocoa ( https://github.com/ReactiveCocoa/ReactiveCocoa ) which use macros from extobjc ( https://github.com/jspahrsummers/libextobjc )

4

An inline method, or a method call aspect might work. This particular macro seems to abuse variadic arguments to the max though.

#define RAC_(TARGET, KEYPATH, NILVALUE) \
[[RACSubscriptingAssignmentTrampoline alloc] initWithTarget:(TARGET) nilValue:(NILVALUE)][@keypath(TARGET, KEYPATH)]

a simple method that takes a selector could work too though, If I read this right.

5

I end up with a helper class:

public static class RAC
{
	public static RACSignal RAC(NSObject target, NSString keypath, RACSignal signal) {
		new RACSubscriptingAssignmentTrampoline(target) nilValue(null).setObject(signal) forKeyedSubscript(keypath);
	}
}

So

RAC(self, createEnabled) = [RACSignal 
    combineLatest:@[ RACObserve(self, password), RACObserve(self, passwordConfirmation) ] 
    reduce:^(NSString *password, NSString *passwordConfirm) {
            return @([passwordConfirm isEqualToString:password]);
}];

Can be wrote as something like:

RAC.RAC(self, "createEnabled", 
    RACSignal.combineLatest( {} ) 
              reduce ( (password, passwordConfirm) => {
	          return passwordConfirm == password;
}));

But it failed to compiled. The method declaration of RACSignal::combineLatest:reduce is:

public static ReactiveCocoa.RACSignal combineLatest(this ReactiveCocoa.RACSignal @this, Foundation.INSFastEnumeration signals) reduce(delegate rtl.id() reduceBlock);

Pls note that reduce take “delegate rtl.id()” as argument. So there’s no way to pass arguments to the block since the signature mismatch.

6

Indeed not. As to your other thread it’s to do with the special block, I’ll have a look at that.