lazy

currentAnimal is an instance property. Instance properties need to have a value when the object is initialised. Either by setting a default value or by setting a value in init(). A lazy property will be set sometime after initialisation (that is the whole point, you don’t want it to have a value until you need it).

The solution depends on what you are trying to achieve. If you need currentAnimal to have a value before viewDidLoad() is called, then you need to make animals an instance property too. Alternatively, you can make it a static property if it can be same for all objects.