Kotlin
Overview
Kotlin is a modern, concise language fully interoperable with Java. Runner Codes provides Kotlin with OpenJDK runtime.
Specifications
| Property | Value |
|---|---|
| Base OS | Debian Bookworm |
| Version | Kotlin 1.9 |
| Rootfs Size | 800 MB |
| Execution | Compiled (kotlinc + kotlin) |
| File Extension | .kt |
| Compile Command | kotlinc Main.kt |
| Run Command | kotlin MainKt |
| Execution Time | ~4.3s |
1. Create Rootfs with infra.operator
sudo infra.operator rootfs create --name kotlin --size 800 --base debian --packages "kotlin"
2. Create Snapshot
sudo infra.operator snapshot create --lang kotlin --mem 512 --vcpus 1
3. Upload rootfs to S3
sudo infra.operator rootfs upload --lang kotlin --bucket runner-codes
3. Upload snapshot to S3
sudo infra.operator snapshot upload --lang kotlin --bucket runner-codes
4. Test Execution
sudo infra.operator host --lang kotlin --code "fun main() { println(\"Hello from Kotlin\") }" --mem 512 --vcpus 1 --snapshot
Examples
Hello World
Request
{
"trace_id": "kotlin-hello-001",
"lang": "kotlin",
"code": "fun main() {\n println(\"Hello from Kotlin!\")\n}",
"timeout": 45
}
Response
{
"trace_id": "kotlin-hello-001",
"stdout": "Hello from Kotlin!\n",
"stderr": "",
"exit_code": 0
}
Data Classes
Request
{
"trace_id": "kotlin-data-001",
"lang": "kotlin",
"code": "data class Person(val name: String, val age: Int)\n\nfun main() {\n val alice = Person(\"Alice\", 30)\n println(\"Name: ${alice.name}\")\n println(\"Age: ${alice.age}\")\n println(alice)\n}",
"timeout": 45
}
Response
{
"trace_id": "kotlin-data-001",
"stdout": "Name: Alice\nAge: 30\nPerson(name=Alice, age=30)\n",
"stderr": "",
"exit_code": 0
}
Null Safety
Request
{
"trace_id": "kotlin-null-001",
"lang": "kotlin",
"code": "fun main() {\n val name: String? = null\n println(name?.length ?: \"Name is null\")\n \n val validName: String? = \"Alice\"\n println(validName?.length ?: \"Name is null\")\n}",
"timeout": 45
}
Response
{
"trace_id": "kotlin-null-001",
"stdout": "Name is null\n5\n",
"stderr": "",
"exit_code": 0
}
Collections
Request
{
"trace_id": "kotlin-coll-001",
"lang": "kotlin",
"code": "fun main() {\n val numbers = listOf(1, 2, 3, 4, 5)\n val squares = numbers.map { it * it }\n val sum = squares.sum()\n \n println(\"Numbers: $numbers\")\n println(\"Squares: $squares\")\n println(\"Sum: $sum\")\n}",
"timeout": 45
}
Response
{
"trace_id": "kotlin-coll-001",
"stdout": "Numbers: [1, 2, 3, 4, 5]\nSquares: [1, 4, 9, 16, 25]\nSum: 55\n",
"stderr": "",
"exit_code": 0
}
Extension Functions
Request
{
"trace_id": "kotlin-ext-001",
"lang": "kotlin",
"code": "fun String.addExclamation(): String = \"$this!\"\n\nfun main() {\n println(\"Hello\".addExclamation())\n println(\"World\".addExclamation())\n}",
"timeout": 45
}
Response
{
"trace_id": "kotlin-ext-001",
"stdout": "Hello!\nWorld!\n",
"stderr": "",
"exit_code": 0
}
Complex Test: Comprehensive Kotlin
Request
{
"trace_id": "kotlin-complex-001",
"lang": "kotlin",
"code": "fun main() {\n println(\"=== Kotlin Complex Test ===\")\n println()\n \n // Test 1: Fibonacci with memoization\n println(\"1. Fibonacci with memoization:\")\n val memo = mutableMapOf<Int, Long>()\n fun fib(n: Int): Long = memo.getOrPut(n) {\n if (n <= 1) n.toLong() else fib(n - 1) + fib(n - 2)\n }\n val fibs = (0..14).map { fib(it) }\n println(\" First 15: $fibs\")\n println(\" Fib(50) = ${fib(50)}\")\n \n // Test 2: QuickSort\n println()\n println(\"2. QuickSort:\")\n fun quicksort(arr: List<Int>): List<Int> {\n if (arr.size <= 1) return arr\n val pivot = arr[arr.size / 2]\n return quicksort(arr.filter { it < pivot }) + arr.filter { it == pivot } + quicksort(arr.filter { it > pivot })\n }\n val unsorted = listOf(64, 34, 25, 12, 22, 11, 90)\n println(\" Input: $unsorted\")\n println(\" Output: ${quicksort(unsorted)}\")\n \n // Test 3: Sealed classes and when\n println()\n println(\"3. Sealed classes and when:\")\n sealed class Animal(val name: String) {\n abstract fun speak(): String\n }\n class Dog(name: String) : Animal(name) {\n override fun speak() = \"$name says Woof!\"\n }\n class Cat(name: String) : Animal(name) {\n override fun speak() = \"$name says Meow!\"\n }\n val animals = listOf(Dog(\"Rex\"), Cat(\"Whiskers\"), Dog(\"Buddy\"))\n animals.forEach { println(\" ${it.speak()}\") }\n \n // Test 4: Collection operations\n println()\n println(\"4. Collection operations:\")\n val numbers = (1..10).toList()\n val squares = numbers.map { it * it }\n val evens = numbers.filter { it % 2 == 0 }\n val sum = squares.sum()\n println(\" Numbers: $numbers\")\n println(\" Squares: $squares\")\n println(\" Evens: $evens\")\n println(\" Sum of squares: $sum\")\n \n // Test 5: Data classes and destructuring\n println()\n println(\"5. Data classes:\")\n data class Person(val name: String, val age: Int, val city: String)\n val people = listOf(\n Person(\"Alice\", 30, \"NYC\"),\n Person(\"Bob\", 25, \"LA\"),\n Person(\"Charlie\", 35, \"Chicago\")\n )\n people.forEach { (name, age, city) -> println(\" $name ($age) from $city\") }\n val byCity = people.associate { it.city to it.name }\n println(\" By city: $byCity\")\n \n // Test 6: Null safety\n println()\n println(\"6. Null safety:\")\n fun divide(a: Int, b: Int): Int? = if (b == 0) null else a / b\n println(\" 10 / 2 = ${divide(10, 2) ?: \"undefined\"}\")\n println(\" 10 / 0 = ${divide(10, 0) ?: \"undefined\"}\")\n val name: String? = null\n println(\" null?.length = ${name?.length ?: \"null\"}\")\n \n // Test 7: Extension functions\n println()\n println(\"7. Extension functions:\")\n fun Int.factorial(): Long {\n var result = 1L\n for (i in 2..this) result *= i\n return result\n }\n fun String.addExclamation() = \"$this!\"\n println(\" 5! = ${5.factorial()}\")\n println(\" 7! = ${7.factorial()}\")\n println(\" \\\"Hello\\\".addExclamation() = ${\"Hello\".addExclamation()}\")\n \n // Test 8: Lambda with receiver\n println()\n println(\"8. Scope functions:\")\n val result = StringBuilder().apply {\n append(\"Hello\")\n append(\", \")\n append(\"World\")\n append(\"!\")\n }.toString()\n println(\" Built string: $result\")\n val lengths = listOf(\"a\", \"bb\", \"ccc\").map { it.length }\n println(\" Lengths: $lengths\")\n \n println()\n println(\"=== All tests passed ===\")\n}",
"timeout": 60
}
Response
{
"trace_id": "kotlin-complex-001",
"stdout": "=== Kotlin Complex Test ===\n\n1. Fibonacci with memoization:\n First 15: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377]\n Fib(50) = 12586269025\n\n2. QuickSort:\n Input: [64, 34, 25, 12, 22, 11, 90]\n Output: [11, 12, 22, 25, 34, 64, 90]\n\n3. Sealed classes and when:\n Rex says Woof!\n Whiskers says Meow!\n Buddy says Woof!\n\n4. Collection operations:\n Numbers: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]\n Squares: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]\n Evens: [2, 4, 6, 8, 10]\n Sum of squares: 385\n\n5. Data classes:\n Alice (30) from NYC\n Bob (25) from LA\n Charlie (35) from Chicago\n By city: {NYC=Alice, LA=Bob, Chicago=Charlie}\n\n6. Null safety:\n 10 / 2 = 5\n 10 / 0 = undefined\n null?.length = null\n\n7. Extension functions:\n 5! = 120\n 7! = 5040\n \"Hello\".addExclamation() = Hello!\n\n8. Scope functions:\n Built string: Hello, World!\n Lengths: [1, 2, 3]\n\n=== All tests passed ===\n",
"stderr": "",
"exit_code": 0
}
Limitations
warning
The Kotlin environment has the following limitations:
- Compilation overhead: kotlinc is slow (~5-7s)
- No external libraries: Only Kotlin standard library
- Memory limit: 512 MiB
- Increase timeout: Use 45+ seconds
Best Practices
Best Practices
- Use data classes — Data classes provide equals, hashCode, toString automatically.
- Handle nullability — Use nullable types (?) and safe calls (?.) properly.
- Use Kotlin idioms — Prefer when expressions over switch, use let/apply/run for scoping.
- Account for compilation — Set timeout to at least 60 seconds for JVM startup.