Kotlin Conventions

Kotlin Conventions

Apply these conventions unless another rule explicitly overrides them.

Class Layout

Organize class contents in this order:

1. Property declarations and initializer blocks
2. Secondary constructors
3. Method declarations
4. Companion object

Do not sort method declarations alphabetically or by visibility, and do not separate regular methods from extension methods. Group related code so that someone reading the class from top to bottom can follow its logic. Choose either higher-level-first or lower-level-first ordering and apply it consistently.

One Top-Level Class Per File

Prefer one top-level class per file. Create additional files when necessary.

Prefer:

Class1.kt

class Class1 {}

Class2.kt

class Class2 {}

Do not use:

Classes.kt

class Class1 {}

class Class2 {}

Lambdas Over Method References

Prefer lambdas over method references. For example, use abc.doSomething { it.abc() } instead of abc.doSomething(Abc::abc).

Inline Unshared Constants

Do not extract constants merely for the sake of extraction. Inline values that are not shared.

Do:

class Class1 {
  fun hello() {
    println("Test")
  }
}

Don't:

class Class1 {
  fun hello() {
    println(TEST_MESSAGE)
  }
}

private const val TEST_MESSAGE = "Test"

Smallest Possible Scope

Use the smallest possible scope for language constructs. For example, nest an extension function used by only one class inside that class rather than declaring it as a private top-level function next to the class.

For an extension function used by one class, do:

class Class1 {
  fun hello() {
    "Test".inConsole()
  }

  private fun String.inConsole() = println(this)
}

Don't:

class Class1 {
  fun hello() {
    "Test".inConsole()
  }
}

private fun String.inConsole() = println(this)

For a constant used by one class, do:

class Class1 {
  fun hello1() {
    println(PROFILE_PICTURE_KEY)
  }

  fun hello2() {
    println(PROFILE_PICTURE_KEY)
  }

  private companion object {
    const val PROFILE_PICTURE_KEY = "profile-picture"
  }
}

Don't:

class Class1 {
  fun hello1() {
    println(PROFILE_PICTURE_KEY)
  }

  fun hello2() {
    println(PROFILE_PICTURE_KEY)
  }
}

private const val PROFILE_PICTURE_KEY = "profile-picture"

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: vRallev
• Source: vRallev/agent-skills
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.