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name: kotlin-best-practices description: Core Kotlin patterns for scope functions, backing properties, and read-only collection interfaces. Use for let/apply/run/also/with choices or encapsulating mutable state; defer general language constructs, extension functions, coroutines/runCatching, Android/Room recipes, and testing/tooling setup. metadata: triggers: files: - '**/*.kt' keywords: - apply - let - run - also - with - runCatching - backing property - MutableList - internal - private set

Kotlin Best Practices

Priority: P1 (HIGH)

Implementation Guidelines

• Scope Functions:
• apply: Object configuration (returns object).
• also: Side effects / validation / logging (returns object).
• let: Null checks (?.let) or mapping (returns result).
• run: Object configuration and mapping (returns result).
• with: Grouping multiple method calls on object (returns result).
• Backing Properties: Use _state (private mutable, e.g., private val _state = MutableStateFlow(initial)) exposed as val state = _state.asStateFlow() (public read-only). Pattern: _prop private, prop public.
• Collections: Expose List/Map (read-only) publicly; keep MutableList internal.
• Error Handling: Use runCatching for simple error handling over try/catch blocks.
• Visibility: Default to private or internal. Minimize public surface area.
• Top-Level: Prefer top-level functions/constants over implementation-less object singletons.

Anti-Patterns

• No Deep Scope Nesting: Limit let/apply nesting to 2 levels; deeper destroys readability.
• No Public var: Use private set or backing properties for encapsulation.
• No Global Mutable State: Avoid mutable top-level variables.

References

• Backing Property & Scope Function Examples