ai

Enforces idiomatic Kotlin over Java-style patterns when writing or reviewing Kotlin code. Use when generating, reviewing, or refactoring Kotlin. Covers scope functions, collections, data/sealed/value classes, extensions, coroutines, and DSL builders.

Parse, don't validate - using sealed classes for type-safe validation and state representation. Model valid/invalid states explicitly, validate at boundaries, operate on valid types internally. Use when implementing validation with sealed classes, modeling valid/invalid states, or applying parse-don't-validate patterns in Kotlin. The pattern is transferrable to other languages, though the mechanism will differ.

Manual dependency injection using SystemContext (production) and TestContext (test doubles) patterns for Kotlin. Use when structuring service dependencies, wiring application components, or creating test contexts without DI frameworks.

Kotlin Test-Driven Development with fakes, object mothers, and Testing Through The Domain. Uses TestContext for dependency injection, extension functions for test data, and fakes instead of mocks. Use when writing Kotlin tests or setting up test infrastructure.