Swift Unwrapping optional class variable yields failure - swift

Question

In my code I have two classes: Reviews and BlogPosts:
class Review {
var author = ""
var stars = 0
}
class BlogPost {
var title = ""
var body = ""
var author = ""
var review: Review?
}
The review variable in BlogPost is optional, since not all blog posts might have a review.
I have a function which prints the amount of stars of a post:
func checkForPostStars(post: BlogPost) {
if let review = post.review {
print("\"\(post.title)\" has: \(review.stars) stars")
} else {
print("There is no review for the post.")
}
}
I then create two blog posts. The first one has no review, meaning that the function should print "There is no review for the post". For the other review I add an author and a star amount, but when I run the function it will still print "There is no review for the post".
var firstPost = BlogPost()
firstPost.title = "Famous developer has died!"
firstPost.body = "Lorem ipsum"
firstPost.author = "Riccardo Perego"
var secondPost = BlogPost()
secondPost.title = "iOS 12 is finally out!"
secondPost.body = "Lorem ipsum"
secondPost.author = "Riccardo Perego"
secondPost.review?.author = "John"
secondPost.review?.stars = 4
checkForPostStars(post: firstPost)
checkForPostStars(post: secondPost)
I have discovered that I can fix the issue by adding secondPost.review = Review() nevertheless, I would like the compiler to do it automatically as soon as it sees that I set a value for stars or author. Thanks.

Answer 1

The problem lies within these 2 lines:
secondPost.review?.author = "John"
secondPost.review?.stars = 4
The review is not initialized. It's like you would set some value to nil and expect it's properties to live even if it doesn't work... That's why the ? is there.
You should add constructor to the Review:
class Review {
var author: String
var stars: Int
init(author: String = "", stars: Int = 0) {
self.author = author
self.starts = stars
}
}
Also it is good practice not to assign the variables on class level scope, rather use it in initialiser.
Simply the problem is that you do not create Review instance, so you cannot add properties to it... you should handle it like this:
secondPost.review = Review(authoer: "John", stars: 4)
Also, for performance reasons, you should make the Review object struct instead of class...
So if you create a struct instead, Swift figures out the initialiser for you and life's even better:
struct Review {
var author: String
var stars: Int
}