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