Tags: the difference of div method option declares type to judge a forced operationOptional type (? ) with the Force parsing operator (!)? is a kind of judgment after unpacking the grammar sugar! is a forced unpacking syntax sugar when you're not sure you have a value, you can use it. You can use it when you're sure you have a value!
?Several usage scenarios:
Implicitly Unwrapped Optionalsvalues, typically used for properties in a class
In Swift? And! The difference