How do I create an extension function in Kotlin, which operates on a class?

Question

Imagine, I have this line of code:

import org.mockito.Mockito
val mock = Mockito.mock(Sim2ParametersProvider::class.java)

I want to be able to write it like this:

val mock = Sim2ParametersProvider::class.mock()

How do I do this?

I tried

fun <T : kotlin.Any> kotlin.reflect.KClass<T>.mock() = Mockito.mock(this)

but it gives me compiler errors.

Not answering your question, but I found the following function to be more useful: `inline fun mock() = Mockito.mock(T::class.java)` Usage: `val foo = mock()`. In many cases you don't even have to write out the type parameter because of type inference. — Kirill Rakhman, Apr 14 '16 at 09:08
Take a look at this nice project: https://github.com/nhaarman/mockito-kotlin — Ruslan, Apr 14 '16 at 10:39

Doug Stevenson · Accepted Answer · 2016-04-14T06:36:17.423

4

It looks like you're slightly mixing up KClass and java Class. The following compiles for me, to extend java classes:

fun <T> Class<T>.mock() = Mockito.mock(this)
val mock1 = FooClass::class.java.mock()

Also the following compiles for me, extending Kotlin KClass:

fun <T: Any> KClass<T>.mock() = Mockito.mock(this.java)
val mock2 = FooClass::class.mock()

Assuming that FooClass is a class, of course.

edited Apr 14 '16 at 06:36

answered Apr 14 '16 at 06:06

Doug Stevenson

1 Answers1