I’ve got a test util for managing a directory and creating files. I want to use a delegate to easily create files

testProject("foo") {
  var otherFileKt by projectFile("other_file.kt")
  otherFileKt = """
    // ...
  """.trimIndent()
}

but I keep getting

Property delegate must have a 'getValue(Nothing?, KProperty*>)' method. None of the following functions are suitable.

what’s wrong with my code?

First parameter of delegate operators is object which property the delegate is (if exists,

null

otherwise). So when you use it to delegate local variable (variable in lambda is also local variable) there is no object which property you delegate, so

thisRef

in

getValue

and

setValue

will be just

null

. To get contextual

ProjectTest

instance you need to provide it explicitly via receiver or context receiver of

projectFile

function. For example:

import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

interface Project

fun project(arg: Project.() -> Unit) {}

class MyDelegate(project: Project, path: String) : ReadWriteProperty<Any?, String> {
    override fun getValue(thisRef: Any?, property: KProperty<*>): String = TODO()
    override fun setValue(thisRef: Any?, property: KProperty<*>, value: String) = TODO()
}

fun Project.file(path: String) : ReadWriteProperty<Any?, String> = MyDelegate(this, path)

fun main() = project {
    val myFile by file("path")
}