For which operation is it mandatory to use reified in Kotlin?

In Kotlin, the keyword reified is essential when working with generic functions that need to access the type of a parameter at runtime. Usually, due to type erasure, information about generic types is unavailable at runtime, but with inline functions and reified, this information can be preserved and used.

A typical example is a function that creates an instance of a class or performs a type check:

inline fun <reified T> isInstance(value: Any): Boolean {
    return value is T
}

val result = isInstance<String>("test") // true

Without reified, it is impossible to use T in the is operator or to access T::class.

Thus, reified is necessary for operations where you need to obtain information about the type of a generic parameter at runtime, such as type checks, creating instances, obtaining class objects, etc.