What is the easiest way to print a Kotlin data class as compilable code? - kotlin

Question

I'd like to be able to turn an instance of a fairly simple Kotlin data class into a String that could be copy and pasted into a Kotlin file and would compile.
For example, given these data classes:
data class Parent(val name: String, val age: Int, val children: Set<Child>)
data class Child(val name: String, val age: Int)
I would like a function from any data class to String such that:
toCompilableString(
Parent("Joe", 34, setOf(Child("Amy", 4), Child("Bob", 7)))
)
would return
"""Parent("Joe", 34, setOf(Child("Amy", 4), Child("Bob", 7)))"""
Does such a thing exist?

Answer 1

We can override the behaviour of toString to output in the desired format:
fun main() {
var amy = Child(name="Amy",age=4)
var bob = Child(name="Bob",age=7)
var joe = Parent(name="Joe", age=34, children=setOf(amy, bob))
print(joe) // outputs "Parent("Joe", 34, setOf(Child("Amy", 4), Child("Bob", 7))"
}
data class Parent(val name: String, val age: Int, val children: Set<Child>) {
override fun toString() = "Parent(\"$name\", $age, setOf(${children.joinToString()})"
}
data class Child(val name: String, val age: Int) {
override fun toString() = "Child(\"$name\", $age)"
}
With the help of joinToString(), this will output in the format "Parent("Joe", 34, setOf(Child("Amy", 4), Child("Bob", 7))".

Answer 2

If you really love pain, there are reflection tools made specially for such things. I made a small function that will generate what you need:
fun dataClassToString(instance: Any) {
val sb = StringBuilder()
sb.append("data class ${instance::class.qualifiedName} (")
var prefix = ""
instance::class.memberProperties.forEach{
sb.append(prefix)
prefix = ","
sb.append("${it.name} = ${it.getter.call(instance)}")
}
sb.append(")")
println(sb.toString())
}
The only problem with this function is that for your parent class it generates the following:
data class Parent (age = 34,children = [Child(name=Amy, age=4), Child(name=Bob, age=7)],name = Joe)
Internally set is represented as array, however if you know for sure that you will have only sets or arrays, you can easily check what type it is and append that type when creating the set. You can also check if this is a data class and append it instead of hardcoded string.