Читать книгу Programming Kotlin Applications - Бретт Мак-Лахлин, Brett McLaughlin - Страница 83

Another easy solution is to explicitly tell Kotlin that you are going to initialize a property later. It's sort of the equivalent of saying, “Look, Kotlin, trust me. I promise I'll take care of this.” To do this, you preface a property declaration with lateinit, a keyword that means what it sounds like—you'll initialize the property in question later:

class Person(_firstName: String, _lastName: String, _height: Double, _age: Int, _hasPartner: Boolean) { lateinit var fullName: String

Remove the assignment to “” and add lateinit. Now, your class will compile again! No problem.

WARNING lateinit has some pretty specific limitations. It only works with var, not val, and the properties can't be declared within the constructor itself. You also can't create a custom accessor or mutator for a lateinit-declared property. So it's not a fix-all. In fact, it's not even a fix in this case, really.

While it might seem this solves your problem, that's not actually true. You still have the same problem as assigning an empty string to fullName : you've built a silent dependence on updateName() being called in init. Kotlin is no longer checking for you, because you said, “I'll take care of it.”

So this is still a fragile solution, and in some cases, even more dangerous than just using a dummy value to start with.