Question

this is my first post; this site has been an invaluable resource.

I’m fairly new to objective-c so please bear with.

So I have a base class with a few properties which I want “private” so I made them readonly. To be clear, I don’t want them mutable externally, but I DO wan’t to use the ‘set’ accessor within this class. So…

// .h file
@interface Vehicle
@property (nonatomic, readonly) int speed;
@end

Also I repeated the property declaration within a category interface block to make the accessors writable in this class

// .m file
//Private properties and methods
@interface Vehicle()
@property (nonatomic, readwrite) int speed;
@end

@implementation
@synthesize speed = _speed;
- (void) someMethod {
    [self setSpeed:10]; // Works fine
}

@end

But now if I inherit this class the derived class no longer has the set accessor method (setSpeed in my case). Do I need to synthesize again? Seems like that would defeat the purpose of inheritence. I know i can modify the instance variable directly (_speed = 10;) but would rather not. I’m sure there’s something wrong with my understanding. Thanks!

// Example
@interface Ship : Vehicle
@end

@implementation
- (void) someOtherMethod {
    [self setSpeed: 2]; // DOES NOT WORK, would like it to
}
@end

Answer 1

But now if I inherit this class the derived class no longer has the set accessor method (setSpeed in my case).

Actually, it does have the set accessor, it’s just that the compiler doesn’t know about it. You have a choice:

• put the class extension (the @interface Vehicle() .... @end bit in a separate header file that gets imported into the .m for Vehicle and its subclasses (or use a category)
• redeclare the read/write property in a class extension for the subclass. To avoid a warning, use @dynamic speed in the subclass’s implementation.