Kotlin DSL example

dragons.kt

class Village(val name: String, val huts: MutableList<Hut>)

class Hut(val address: String,
          val vikings: MutableList<Viking>,
          val dragons: MutableList<Dragon>)

class Viking(val name: String)

class Dragon(val name: String)

dragons_dsl_marker1.kt

// Main.kt
val berk = village(name = "Berk") { // <- VillageBuilder
    hut(address = "13 Wings Avenue") { // <- HutBuilder
        viking("Bjorn")
        dragon("Toothless")
        dragon("Gruff")
        dragon("Cloud Jumper")
        hut { /* <- we shouldn't be able to */ }
    }
    hut {
        address = "8 Ball St"
        viking("Ragnar")
        viking("Helga")
        dragon("Scrill")
    }
}

dragons_dsl_marker2.kt

@DragonDSL
class VillageBuilder(/* ... */)

@DragonDSL
class HutBuilder(/* ... */)

@DslMarker
annotation class DragonDSL

// Main.kt
val berk = village(name = "Berk") { // <- VillageBuilder
    hut(address = "13 Wings Avenue") { // <- HutBuilder
        viking("Bjorn")
        dragon("Toothless")
        dragon("Gruff")
        dragon("Cloud Jumper")
        [email protected] { /* <- we can do it but only with explicit receiver */ }
    }
    hut {
        address = "8 Ball St"
        viking("Ragnar")
        viking("Helga")
        dragon("Scrill")
    }
}

dragons_dsl_optimization.kt

package dragons

// DragonDSL.kt
fun village(name: String, init: VillageBuilder.() -> Unit): Village {
    return VillageBuilder(name).apply(init).build()
}

@DragonDSL
class VillageBuilder(private val name: String) {
    private val huts = mutableListOf<Hut>()

    fun build() = Village(name, huts)

    fun hut(address: String = "", init: HutBuilder.() -> Unit) {
        huts.add(HutBuilder(address).apply(init).build())
    }
}

@DragonDSL
class HutBuilder(var address: String = "") {
    private val vikings = mutableListOf<Viking>()
    private val dragons = mutableListOf<Dragon>()
    fun build(): Hut = Hut(address, vikings, dragons)

    fun viking(name: String) {
        vikings.add(Viking(name))
    }
    fun vikings(vararg names: String) {
        vikings.addAll(names.map { Viking(it) })
    }
    fun dragon(name: String) {
        dragons.add(Dragon(name))
    }
    fun dragons(vararg names: String) {
        dragons.addAll(names.map { Dragon(it) })
    }
}

@DslMarker
annotation class DragonDSL

// Main.kt
val berk = village(name = "Berk") { // <- VillageBuilder
    hut(address = "13 Wings Avenue") { // <- HutBuilder
        viking("Bjorn")
        dragons("Toothless", "Gruff", "Cloud Jumper")
    }
    hut {
        address = "8 Ball St"
        vikings("Ragnar", "Helga")
        dragon("Scrill")
    }
}

dragons_dsl_step1.kt

// DragonDSL.kt
fun village(init: VillageBuilder.() -> Unit): Village {
    return VillageBuilder().apply(init).build()
}

class VillageBuilder {
    fun build(): Village {
        TODO("not implemented")
    }
}

// Main.kt
val berk = village { // <- VillageBuilder
  
}

dragons_dsl_step2.kt

// DragonDSL.kt
fun village(init: VillageBuilder.() -> Unit): Village {
    return VillageBuilder().apply(init).build()
}

class VillageBuilder {
    private val huts = mutableListOf<Hut>() 
    fun build(): Village {
        TODO("not implemented")
    }
    fun hut(init: HutBuilder.() -> Unit) {
        huts.add(HutBuilder().apply(init).build())  
    } 
}

class HutBuilder {
    fun build(): Hut {
        TODO("not implemented")
    }
}

// Main.kt
val berk = village { // <- VillageBuilder
    hut { // <- HutBuilder
        
    }
}

dragons_dsl_step3.kt

// DragonDSL.kt
fun village(name: String, init: VillageBuilder.() -> Unit): Village {
    return VillageBuilder(name).apply(init).build()
}

class VillageBuilder(private val name: String) {
    private val huts = mutableListOf<Hut>()
    
    fun build() = Village(name, huts)
    
    fun hut(init: HutBuilder.() -> Unit) {
        huts.add(HutBuilder().apply(init).build())
    }
}

class HutBuilder {
    fun build(): Hut {
        TODO("not implemented")
    }
}

// Main.kt
val berk = village(name = "Berk") { // <- VillageBuilder
    hut { // <- HutBuilder

    }
}

dragons_dsl_step4.kt

// DragonDSL.kt
fun village(name: String, init: VillageBuilder.() -> Unit): Village {
    return VillageBuilder(name).apply(init).build()
}

class VillageBuilder(private val name: String) {
    private val huts = mutableListOf<Hut>()

    fun build() = Village(name, huts)

    fun hut(init: HutBuilder.() -> Unit) {
        huts.add(HutBuilder().apply(init).build())
    }
}

class HutBuilder {
    private val vikings = mutableListOf<Viking>()
    private val dragons = mutableListOf<Dragon>()
    fun build(): Hut = Hut("", vikings, dragons)

    fun viking(name: String) {
        vikings.add(Viking(name))
    }
    fun dragon(name: String) {
        dragons.add(Dragon(name))
    }
}

// Main.kt
val berk = village(name = "Berk") { // <- VillageBuilder
    hut { // <- HutBuilder
        viking("Bjorn")
        dragon("Toothless")
        dragon("Gruff")
        dragon("Cloud Jumper")
    }
    hut {
        viking("Ragnar")
        viking("Helga")
        dragon("Scrill")
    }
}

dragons_dsl_step5_final.kt

// DragonDSL.kt
fun village(name: String, init: VillageBuilder.() -> Unit): Village {
    return VillageBuilder(name).apply(init).build()
}

class VillageBuilder(private val name: String) {
    private val huts = mutableListOf<Hut>()

    fun build() = Village(name, huts)

    fun hut(address: String = "", init: HutBuilder.() -> Unit) {
        huts.add(HutBuilder(address).apply(init).build())
    }
}

class HutBuilder(var address: String = "") {
    private val vikings = mutableListOf<Viking>()
    private val dragons = mutableListOf<Dragon>()
    fun build(): Hut = Hut(address, vikings, dragons)

    fun viking(name: String) {
        vikings.add(Viking(name))
    }
    fun dragon(name: String) {
        dragons.add(Dragon(name))
    }
}

// Main.kt
val berk = village(name = "Berk") { // <- VillageBuilder
    hut(address = "13 Wings Avenue") { // <- HutBuilder
        viking("Bjorn")
        dragon("Toothless")
        dragon("Gruff")
        dragon("Cloud Jumper")
    }
    hut {
        address = "8 Ball St"
        viking("Ragnar")
        viking("Helga")
        dragon("Scrill")
    }
}

dragons_not1.kt

val vikings1 = mutableListOf(Viking("Bjorn"))
val vikings2 = mutableListOf(Viking("Ragnar"), Viking("Helga"))

val dragons1 = mutableListOf(
        Dragon("Toothless"),
        Dragon("Gruff"),
        Dragon("Cloudjumper"))

val dragons2 = mutableListOf(Dragon("Scrill"))

val huts = mutableListOf(
        Hut("13 Wings Avenue", vikings1, dragons1),
        Hut("8 Ball St", vikings2, dragons2)
)

val firstVillage = Village("Berk", huts)

dragons_not2.kt

val secondVillage = Village("Berk",
        mutableListOf(
                Hut("13 Wings Avenue",
                        mutableListOf(Viking("Bjorn")),
                        mutableListOf(
                            Dragon("Toothless"),
                            Dragon("Gruff"),
                            Dragon("Cloudjumper"))
                ),
                Hut("8 Ball St",
                        mutableListOf(Viking("Ragnar"), Viking("Helga")),
                        mutableListOf(Dragon("Scrill")))
        )
)

dslexample1.1.kt

class Foo {
    fun test() {
        println("testing bar!")
    }
}

fun fooCreator(): Foo {
    return Foo()
}

fun higherOrderFun(functionRef: () -> Foo) {
    functionRef().test()
}

dslexample1.2.kt

fun main(args: Array<String>) {
    higherOrderFun(::fooCreator)

    higherOrderFun({ Foo() })

    higherOrderFun { Foo() }
}

dslexample2.1.kt

class Foo(val message: String) {
    fun test() {
        println(message)
    }
}

fun fooCreator(message: String): Foo {
    return Foo(message)
}

fun higherOrderFun(functionRef: (String) -> Foo) {
    functionRef("From fun").test()
}

dslexample2.2.kt

fun main(args: Array<String>) {
    higherOrderFun(::fooCreator)
    higherOrderFun { Foo("From main") }
}

dslexample3.1.kt

class Foo(val message: String)

fun Foo.test() {
    println(message)
}

fun higherOrderFun(foo: Foo, functionRef: Foo.() -> Unit) {
    foo.functionRef()
}

dslexample3.2.kt

fun main(args: Array<String>) {
    higherOrderFun(Foo("From main"), Foo::test)

    higherOrderFun(Foo("Another example"), { println("Custom: ${message}") })

    higherOrderFun(Foo("Another example")) {
        println("Custom: $message")
    }
}