Kotlin DSL for collections - kotlin

Question

This is a simple data structure House which contains a (nullable) list of Person :
data class Person(val name: String,
val militaryYear: Int? = null,
val firstPregnantYear: Int? = null)
data class House(val persons: List<Person>?)
Person maybe male or female. Male has militaryYear value , Female has firstPregnantYear value.
I want to write a DSL to build the House object , like this :
val house = house {
person("John") {
militaryYear = 2003
}
person("Anne") {
firstPregnantYear = 2010
}
}
This is what I have done :
data class Person(val name: String,
val militaryYear: Int? = null,
val firstPregnantYear: Int? = null) {
class Builder(private val name: String) {
var militaryYear : Int? = null
var firstPregnantYear : Int? = null
fun build(): Person = Person(name, militaryYear, firstPregnantYear)
}
}
fun person(name: String , block: Person.Builder.() -> Unit) = Person.Builder(name).apply(block).build()
data class House(val persons: List<Person>?) {
class Builder {
var persons = mutableListOf<Person>()
fun person(name: String , block: Person.Builder.() -> Unit) {
persons.add(Person.Builder(name).apply(block).build())
}
fun build(): House = House(persons = persons.takeIf { it.isNotEmpty() })
}
}
It seems works , but it doesn't forbid both militaryYear & firstPregnantYear , for example :
val house = house {
person("John") {
militaryYear = 2003
}
person("Anne") {
firstPregnantYear = 2010
}
person("Alien") {
militaryYear = 2005
firstPregnantYear = 2009
}
}
println(house)
The result :
House(persons=[
Person(name=John, militaryYear=2003, firstPregnantYear=null)
, Person(name=Anne, militaryYear=null, firstPregnantYear=2010)
, Person(name=Alien, militaryYear=2005, firstPregnantYear=2009)
])
The Alien has militaryYear & firstPregnantYear , which is incorrect.
So , I add another MaleBuilder and FemaleBuilder :
class MaleBuilder(private val name: String) {
var militaryYear = 0
fun build(): Person = Person(name, militaryYear, null)
}
class FemaleBuilder(private val name: String) {
var firstPregnantYear = 0
fun build() : Person = Person(name , null , firstPregnantYear)
}
fun male(name: String , block: Person.MaleBuilder.() -> Unit) = Person.MaleBuilder(name).apply(block).build()
fun female(name: String , block: Person.FemaleBuilder.() -> Unit) = Person.FemaleBuilder(name).apply(block).build()
And the DSL becomes :
val house = house {
male("John") {
militaryYear = 2003
}
female("Anne") {
firstPregnantYear = 2010
}
}
println(house)
OK , here is the problem , male("John") and female("Anne") are not inserted into persons . It outputs :
House(persons=null)
I think the problem comes from House's person() function :
fun person(name: String , block: Person.Builder.() -> Unit) {
persons.add(Person.Builder(name).apply(block).build())
}
The defined receiver is Person.Builder , but it is MaleBuilder and FemaleBuilder in the code.
How to solve this problem ?
Full code : https://pastebin.com/1Q6D8rzx
------- updated -------
It can be solved by introducing House.Builder.male() and House.Builder.female() functions :
fun male(name: String , block: Person.MaleBuilder.() -> Unit) {
persons.add(Person.MaleBuilder(name).apply(block).build())
}
fun female(name: String , block: Person.FemaleBuilder.() -> Unit) {
persons.add(Person.FemaleBuilder(name).apply(block).build())
}
But I think it is not a good solution. In real world example , there maybe a lot of properties , and a lot of restrictions. Is there a way to use one function to receive it ?