Why DSLs improve readability in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a simple DSL function that prints a greeting.

Kotlin

fun greet() {
    println([1])
}

greet()

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Aprintln("Hello")

BHello, DSL!

C"Hello, DSL!"

Dgreet

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around the greeting text.

Passing a function name instead of a string.

The println function needs a string argument, so the greeting must be in quotes.

2fill in blank

medium

Complete the code to create a DSL builder function that adds two numbers.

Kotlin

fun addNumbers(block: () -> Int): Int {
    return [1]()
}

val result = addNumbers { 5 + 3 }
println(result)

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AaddNumbers

Bblock

Cprintln

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to return the function name without calling it.

Using println instead of calling the block.

The block parameter is a function that returns an Int, so calling block() executes it.

3fill in blank

hard

Fix the error in the DSL function that builds a greeting message.

Kotlin

fun greeting(block: GreetingBuilder.() -> Unit): String {
    val builder = GreetingBuilder()
    builder.[1](block)
    return builder.message
}

class GreetingBuilder {
    var message = ""
    fun sayHello() {
        message = "Hello from DSL!"
    }
}

println(greeting { sayHello() })

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Aapply

Brun

Cinvoke

Dcall

Attempts:

3 left

💡 Hint

Common Mistakes

Using run which returns the block result instead of the object.

Trying to call invoke or call which are not applicable here.

The apply function runs the block with the receiver and returns the receiver object.

4fill in blank

hard

Fill both blanks to create a DSL that builds a list of strings with a custom builder.

Kotlin

class StringListBuilder {
    val items = mutableListOf<String>()
    fun add(item: String) { items.[1](item) }
}

fun buildList(block: StringListBuilder.() -> Unit): List<String> {
    val builder = StringListBuilder()
    builder.[2](block)
    return builder.items
}

val list = buildList {
    add("apple")
    add("banana")
}
println(list)

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Aadd

Bapply

Cremove

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove instead of add to add items.

Using run instead of apply which returns the object.

The add function adds an item to the list, and apply runs the block on the builder object.

5fill in blank

hard

Fill all three blanks to create a DSL that builds a map with keys and values.

Kotlin

class MapBuilder {
    val map = mutableMapOf<String, Int>()
    fun put(key: String, value: Int) { map.[1](key, value) }
}

fun buildMap(block: MapBuilder.() -> Unit): Map<String, Int> {
    val builder = MapBuilder()
    builder.[2](block)
    return builder.[3]
}

val result = buildMap {
    put("one", 1)
    put("two", 2)
}
println(result)

Drag options to blanks, or click blank then click option'

Aput

Bapply

Cmap

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using run instead of apply which returns the builder.

Returning the builder instead of the map property.

Using add instead of put for the map.

The put method adds entries to the map, apply runs the block on the builder, and map returns the built map.