RACCommand compilation failure on swift 1.2 - ios

Question

I have a login button with a RACCommand assigned to it to perform a login request and return me a user object.
I want to handle the errors from the buttons signal errors.
loginButton.rac_command.executionSignals.flatten()
.logAll()
.subscribeNext { (_:AnyObject!) -> Void in
println("Sent next")
}
so i added the doError block before the subscribeNext block but now the code doesn't compile:
loginButton.rac_command.executionSignals.flatten()
.logAll()
.doError { (err:NSError) -> Void in
println(err.description)
}
.subscribeNext { (_:AnyObject!) -> Void in
println("Sent next")
}
Now it comes back with the error:
cannot invoke 'subscribeNext' with an argument list of type '(AnyObject! -> Void)'
Since the signature of doError is :
- (RACSignal *)doError:(void (^)(NSError *error))block;
I'm assuming that its giving me back the same signal that was passed to the doError block so i can subscribeNext to it.
Not sure why this fails to compile at all though.
Any insight to this issue is much appreciated.

Answer 1

Typo is in argument of doError() (and incorrectly identified by compiler): it should be of type (NSError!) -> Void instead of (NSError) -> Void. Modified like this it compiles fine:
loginButton.rac_command.executionSignals.flatten()
.logAll()
.doError { (err:NSError!) -> Void in
println(err.description)
}
.subscribeNext { (_:AnyObject!) -> Void in
println("Sent next")
}
Additional remarks
Errors from RACCommand are caught internally and sent on errors()
signal, so none are sent on executionSignals() signal.
doNext(), doError(), doComplete() methods are to be used for
injecting side effects to the signal. So you typically use them while
creating signal, not when handling its events. You might want to use
subscribeNext(nextBlock:error:completed:) method (or one of its convenience forms) instead.