Is reflection being used when using the 'is' operator in Kotlin

Question

As MVI is getting more and more popular in Android development, the use of Sealed classes increases as well. And we know that we have to determine the actual type of the Sealed class in order to continue with a particular flow from our logic.

So does Kotlin use reflection when using the 'is' operator for type checks? Tried to go through the documentation, but couldn't find anything about that. https://kotlinlang.org/docs/typecasts.html

Answer 1

Depends on the definition of reflection you're using. Often “reflection” in the JVM world is used to describe specifically the String-based code meta data inspection from the java.lang.reflect package (or Kotlin reflection dependency) that is considered to be inefficient. But a more general definition of “reflection” is any code introspection. is arguably fits the second definition, but it is fast/optimized and not part of the first definition.

Answer 2

The 'is' operator in Kotlin is used for type checks, for example to check if an object is an instance of a particular class or its subclasses. The 'is' operator does not use reflection to perform type checks. Instead, the type check is done at compile-time, and the generated bytecode contains an instanceof check, which is a standard JVM instruction for performing type checks.

In the case of sealed classes, the use of 'is' operator will not use reflection as well, it's a compile-time check, that's why when using the 'is' operator with a sealed class, the compiler is able to perform type checks and generate the appropriate bytecode at compile-time.

Using the 'is' operator is much more efficient than using reflection, as it is a compile-time check and it does not require any runtime overhead, while reflection can be relatively slow, as it requires the JVM to perform additional lookups and checks at runtime.

So, in summary, the 'is' operator in Kotlin does not use reflection for type checks. It's a compile-time check, which is much more efficient than using reflection.