Quick Answer

Deferred initialization of non-null properties

Understanding the Issue

lateinit allows non-null properties to be initialized after construction but before use. The property must be mutable (var) and cannot have a custom getter/setter.

The Problem

This code demonstrates the issue:

Kotlin Error 
// Problem: Accessing uninitialized lateinit
lateinit var service: Service
fun useService() {
    service.connect() // Crash if not initialized
}

The Solution

Here's the corrected code:

Kotlin Fixed 
// Solution 1: Initialize before use
fun initService(s: Service) {
    service = s
}

// Solution 2: Check initialization
fun useService() {
    if (::service.isInitialized) {
        service.connect()
    }
}

// Solution 3: Consider dependency injection

Key Takeaways

Ensure lateinit properties are initialized before access.