let-guard.swift

class Author {
    var name = ""
    
    init(name: String) {
        self.name = name
    }
}

class Book {
    var author : Author? = nil
    func setAuthor(author: Author) {
        self.author = author
        print("Author set to \(author.name)")
    }
}

let foo : Book? = Book()
let bar : Author? = Author(name: "Bob")

func letIndentationHell(foo: Book?, bar: Author?) {
    if let book = foo {
        if let author = bar {
            book.setAuthor(author)
        }
    }
}

func multipleBind(foo: Book?, bar: Author?) {
    if let book = foo, let author = bar {
        book.setAuthor(author)
    }
}

func objcStyle(foo: Book?, bar: Author?) {
    if (foo == nil || bar == nil) {
        return
    }
    let book = foo!
    let author = bar!
    book.setAuthor(author)
    // or force unwrap both directly with
    // foo!.setAuthor(bar!)
}

func swiftGuardStyle(foo: Book?, bar: Author?) {
    guard let book = foo, author = bar else {
        return
    }
    book.setAuthor(author)
}

func swiftGuardStyle2(book: Book?, author: Author?) {
    guard let book = book, author = author else {
        return
    }
    book.setAuthor(author)
}

func swiftGuardStyleWhere(book: Book?, author: Author?, rating: Int) {
    guard rating > 4, let book = book, author = author where author.name == "Bob" else {
        return
    }
    book.setAuthor(author)
}

letIndentationHell(foo, bar: bar)
multipleBind(foo, bar: bar)
objcStyle(foo, bar: bar)
swiftGuardStyle(foo, bar: bar)
swiftGuardStyle2(foo, author: bar)
swiftGuardStyleWhere(foo, author: bar, rating: 10)