CODEWITHSUNDEEP
objective-ccompiler-errorsprotocols
user1118019
user1118019

Reputation: 3959

Compiler error "expected a type" in protocol definition

I have two files defining protocols, for implementing the observer pattern, and I'm getting a compiler error from one of them.

// ObserverDelegate.h
#import <Foundation/Foundation.h>


@protocol ObserverDelegate <NSObject>
@required
@end


// ObservableDelegate.h
#import <Foundation/Foundation.h>
#import "ObserverDelegate.h"
@protocol ObservableDelegate <NSObject>
@required
-(void) addObserver: (ObservableDelegate*) observer; // ERROR ON THIS LINE WHEN COMPILE
@end

I only have .h files for ObserverDelegate and ObservableDelegate, there are no corresponding .m files.

The error says "expected a type" in ObserveableDelegate.h on the line -(void) addObserver: (ObservableDelegate*) observer;

Upvotes: 1

Views: 3099

Answers (1)

jscs
jscs

Reputation: 64002

ObservableDelegate isn't a type, it's the name of the protocol. You can't use it as the type of a method parameter. If you want to require that the argument to the method conform to that protocol, you express it like this:

- (void)addObserver: (id<ObservableDelegate>)observer;

This says that the method takes any object (id is the "generic" pointer) which conforms to ObservableDelegate. You can use a more specific type than id if you want and you know, for example, that the delegate should always be a UIViewController subclass as well.

Upvotes: 8

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