Is there any difference between `is` operator and ...

# getting-started

[Tim Abil]

Is there any difference between is operator and class comparison?

sealed class MyClass {
    object ONE : MyClass()
    object TWO : MyClass()
}

inline fun <reified T> List<MyClass>.findClass(): T? {
    return find { it is T } as T
}

fun <T: Any> List<MyClass>.findClass(clazz: KClass<T>): T? {
    return find { it::class == clazz } as T?
}

[ephemient]

if there can be subclasses, then there is a difference. in this case there practically isn't as singleton objects cannot be extended

[Casey Brooks]

Yes, the is operator will check the entire class hierarchy to see if any superclasses/interfaces of an object is the T type (bascally, whether you can cast the object to T without throwing a ClassCastException).

Checking the class through == will only check the object's own class type.

This example might help you see the difference https://pl.kotl.in/Rrr-UsLlz

[ephemient]

on a different note, if you wrote

inline fun <reified T : Any> Iterable<*>.findClass(): T? =
    firstNotNullOfOrNull { it as? T }

in Kotlin 1.5+, or

filterIsInstance<T>().firstOrNull()

in older versions, then you don't need the additional cast after finding an element

[Tim Abil]

ahh gotcha thank you!

[Casey Brooks]

It's also worth noting that the is operator can be a relatively expensive check, especially if the class hierarchy is large. The == check is basically going to be a simple object identity check (===) since Class objects are singletons, which is very quick