Kotlin Best Practices

Priority: P1 (HIGH)

Engineering standards for clean, maintainable Kotlin systems.

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 an object (returns result).
• Backing Properties: Use _prop (private mutable) and prop (public immutable) pattern for encapsulation.
• Collections: Expose List/Map (read-only interfaces) publicly, keep MutableList internal.
• Single Expression: 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

• Nesting Scope Functions: Avoid nesting let/apply more than 2 levels deep. It destroys readability.
• Mutable Public Props: Avoid public var. Use private set or backing properties.
• Global Mutable State: Avoid top-level mutable variables.

Code

// Backing Property Pattern
class ViewModel {
    private val _uiState = MutableStateFlow(UiState.Loading)
    val uiState: StateFlow<UiState> = _uiState.asStateFlow() // Read-only

    fun load() {
        // apply for config
        val user = User().apply {
            name = "John"
            age = 30
        }

        // runCatching
        runCatching { api.fetch() }
            .onSuccess { _uiState.value = UiState.Success(it) }
            .onFailure { logger.error(it) }
    }
}

Related Topics

language | coroutines