Is there a way to assert the compile time type of ...

# kotest

[Rob Elliot]

Is there a way to assert the compile time type of an expression?

(I don't want a test that passes because the runtime type of the result of the expression is a subtype of the requested type - I want to assert exactly what type the compiler decided the expression had. When doing overloading with subtypes and overriding with more specific return types it's important.)

[christophsturm]

why not val x: ExpectedType = expression ? that will fail at compile time

[Rob Elliot]

If expression returns a subtype of ExpectedType that will pass. So in order to prove the compile time return type is ExpectedType, not a subtype of ExpectedType, I need to use shouldNotCompile with every single subtype of ExpectedType.

Which is a bit of a pain.

[Rob Elliot]

I'm experimenting with io.kotest.matchers.reflection.shouldHaveReturnType - might give me what I need.

[Rob Elliot]

Yup, that works. Needs kotlin-reflect on the classpath, but then you can do:

import io.kotest.matchers.reflection.shouldHaveReturnType
import kotlin.reflect.jvm.reflect

{ expression }.reflect().shouldNotBeNull().shouldHaveReturnType<ExpectedType>()