Kotlin can be very handy and easy to use. Kotlin offers the possibility to develop code that is easy to understand, safe, immutable, and thus predictable and follows standards that avoid side effects. I realized that very quickly after I started my Kotlin journey that already amounts to more than 4 years.

Having said that, some concepts can be difficult to visualize which can generate some confusion. While there are several advantages to using Kotlin, those advantages can only be put into practice if we can understand what the JVM is doing to our code. There are situations that may seem to question of non-nullable mark offered by Kotlin, others where you'll find functionalities that may seem to serve no purpose at first glance and if you are coming from the Java world you may find confronting the concept of specifically tail-recursive fuctions and its usages. All of these situations have created some confusing situations professionally, generating delays in development, that could have been mitigated if we had previous clear understanding of these concepts.

In this presentation, we are going to have a look at what tailrec, inline, crossinline, nullables, non-nullables do to our code, how the JVM responds to that, and how annotations affect behavior in the Kotlin code for web application services frameworks like the Spring Framework. We'll also have a look at what happens when a non-nullable becomes null in Kotlin and why that happens. You' ll leave this session with these mysteries behind you and ready to face the engineering world with Kotlin by your side whether you venture into android or server side development.