Lazy init. Initialize the value of a variable only when it's first needed

lazy-init.m

@interface MyClass()
// Lazy inits are perfect for readonly values
// Note that strong can be used instead of copy here because
// we control the creation of the array and don't have to worry about
// being passed a mutable version
@property(nonatomic, readonly, strong) NSArray *values;
@end

@implementation MyClass

// Always use explicit synthesize when overriding a getter or setter
@synthesize values = _values;

- (id)init {
  self = [super init];
  
  if (self) {
    // The initializer is the other candidate for 
    // creating the _values array. The benefit of using a lazy 
    // init is that the value is only created if needed.
    //_values = @[@1, @2, @3];
  }
  
  return self;
}

- (NSArray *)values {
  if (!_values) { // Initialize only the first time and only if the property is needed
    _values = @[@1, @2, @3];
  }

  return _values;
}


@end