gistfile1.m

/**
 Provides the ability to verify key paths at compile time.
 
 If "keyPath" does not exist, a compile-time error will be generated.
 
 Example:
    // Verifies "isFinished" exists on "operation".
    NSString *key = SQKeyPath(operation, isFinished);
 
    // Verifies "isFinished" exists on self.
    NSString *key = SQSelfKeyPath(isFinished);
 
    // Verifies "isFinished" exists on instances of NSOperation.
    NSString *key = SQTypedKeyPath(NSOperation, isFinished);
 */
#define SQKeyPath(object, keyPath) ({ if (NO) { (void)((object).keyPath); } @#keyPath; })

#define SQSelfKeyPath(keyPath) SQKeyPath(self, keyPath)
#define SQTypedKeyPath(ObjectClass, keyPath) SQKeyPath(((ObjectClass *)nil), keyPath)
#define SQProtocolKeyPath(Protocol, keyPath) SQKeyPath(((id <Protocol>)nil), keyPath)

/**
 To use SQClassKeyPath, your implementation (.m) file should have a line like this (I usually 
 put it after the @implementation in question):
    typedef MyClass ISFKeyPath_CLASS;

 Or if you have multiple classes defined in one .m file, you can use a macro, which you can undef.
    #undef ISFKeyPath_CLASS
    #define ISFKeyPath_CLASS MyClass

 Example:
    + (NSSet *)keyPathsForValuesAffectingDependentKey
    {
        return [NSSet setWithObjects: SQClassKeyPath(dependedUponKey1), 
                                      SQClassKeyPath(dependedUponKey2), 
                                      nil];
    }
 */
#define SQClassKeyPath(keyPath) SQTypedKeyPath(SQKeyPath_CLASS, keyPath)