Question

When we create core data object automatically I see a line

@synthesize managedObjectContext=__managedObjectContext;

However, I do not think we will ever need that line because the code also generate a function

- (NSManagedObjectContext *)managedObjectContext
{
    if (__managedObjectContext != nil)
    {
        return __managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil)
    {
        __managedObjectContext = [[NSManagedObjectContext alloc] init];
        [__managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return __managedObjectContext;
}

So what am I missing here?

Why synthesize a code that we DO write?

Answer 1

The @synthesize directive

…tell[s] the compiler that it should synthesize the setter and/or getter methods for a property if you do not supply them within the @implementation block.

You’re still allowed to create your own implementations.

So why use @synthesize? To associate the variable (storage) called __managedObjectContext with the property (public access point) called managedObjectContext.

Why do this? As Henrik noted, so that you can do lazy setup of the storage.