You can read more about it in Kotlin docs: typecasts, null-safety.Īnd it’s all great, don’t get me wrong! This behaviour is a lot better than the plain old “every reference can be null, just crash if it is and it’ll be fine”.

Basically, if you check that a variable is not null (or has a particular type), then the compiler changes type of the variable in the block, where the check holds. The “special kotlin trick” is called “smart cast”. (The same applies for calling a function with an argument of non-nullable type, you need to either check that something is not null or explicitly assume so) in this block `mine` actually has type `Mine`. safe call operator, if `mine` is null, given a class Mine with a cat field and a variable mine of type Mine?, you can’t access mine.cat, it would be a compilation error: val mine: Mine? = /*. If you really want to assign null to something, you need to explicitly mark the type of the variable as nullable with T? syntax: // okīut when you have a T? (nullable) type, you also need to explicitly check for null. For example, this is a compilation error: // compilation errorĪnd since you can’t assign null to non-nullable types, null can’t screw you! You can’t get a null pointer (reference) exception, etc. I’m more familiar with Kotlin than C#, so I’ll mostly be talking about it, but their approaches are similar, so that doesn’t really matter.īasically, you can’t assign null to just any reference type in Kotlin (and C# post v8 with certain settings). In this article, I’m specifically talking about the Kotlin and C# post v8 approach to null. But it’s only so bad when it’s not checked by anyone and the compiler doesn’t force you to check it, right? Well, the title might be a spoiler, but let’s find out… Context / What are you talking about? ⌗ We all know that null is a “billion-dollar mistake”, that it creates a lot of easy ways to make terrible mistakes.

Kotlin assign if not null