I’ve got a test util for managing a directory and ...

# getting-started

[Adam S]

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?

[Adam S]

delegateExample_kt.cpp

delegateExample_kt.cpp

[Adam S]

I always find the delegate stuff so confusing, and I don’t find the messages/suggestions from IntelliJ very helpful.

[Adam S]

apparently sometimes the delegate needs to implement

ReadWriteProperty<Any?, String>

and sometimes

ReadWriteProperty<ProjectTest, String>

🤷‍♀️

[Adam S]

delegate2.kt.cpp

delegate2.kt.cpp

[Gleb Minaev]

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")
}