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kotlin-language

Write idiomatic Kotlin 1.9+ with null safety, sealed classes, data classes, extension functions, delegates, collections, inline/reified generics, and expression syntax. Use for Kotlin language constructs, Java-to-Kotlin migration, lazy delegates, data classes, backing properties, or inline/reified generics; keep language constructs in scope even inside response models, and defer coroutine configuration, Android Context/framework, Retrofit/OkHttp client setup, and other library-specific recipes.

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  • SKILL.md2.2 KB
  • evals/evals.json3.3 KB
  • references/example.md1.6 KB

SKILL.md (original)

Review the instructions the agent will receive before you install.

Kotlin Language Patterns

Priority: P0 (CRITICAL)

Implementation Guidelines

  • Immutability: Use val by default. Only use var if mutation required locally.
  • Null Safety: Use ? for nullable types. Use safe call ?. and Elvis ?: over !!.
  • Expressions: Prefer expression bodies fun foo() = ... for one-liners. Use if/try as expressions.
  • Classes: Use data class for DTOs. Use sealed interface/class for state hierarchies (e.g., Success, Error, Loading). Access members as computed property rather than function.
  • Extension Functions: Prefer over utility classes (StringUtil). Keep private/internal if module-specific.
  • Named Arguments: Use for clarity, especially with booleans or multiple same-type params.
  • String Templates: Use "$var" over concatenation. Use "" for multiline strings (SQL/JSON).

Anti-Patterns

  • No !! Operator: Never use in production; prefer safe calls or requireNotNull.
  • No Java-isms: Use properties not get/set; prefer top-level functions over companion object statics.
  • No Lateinit Abuse: Prefer nullable types or lazy delegates instead.
  • No Silenced Errors: Never swallow exceptions without logging or handling.

References

Canonical response anchors

  • Additional task-grounded exact anchors: data class

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