kotlin-development
Kotlin development guidelines with best practices for clean code, naming conventions, function design, and data handling
Works with
--- name: kotlin-development description: Kotlin development guidelines with best practices for clean code, naming conventions, function design, and data handling license: Apache-2.0 --- # Kotlin Development Best Practices ## General Principles - Use English for all code and documentation - Always declare the type of each variable and function - Avoid the `any` type; create necessary types instead - No blank lines within function bodies ## Naming Conventions ### Case Standards - **PascalCase**: Classes, interfaces, enums - **camelCase**: Variables, functions, methods, parameters - **UPPERCASE**: Environment variables, constants - **underscores_case**: Files and directories ### Naming Guidelines - Start each function with a verb (get, set, create, update, delete, etc.) - Use complete words over abbreviations - Allowed abbreviations: API, URL, i/j for loops, err, ctx, req/res/next - Avoid magic numbers; define constants instead - Boolean variables use prefixes: `isLoading`, `hasError`, `canDelete` ## Function Design ### Size and Responsibility - Keep functions under 20 instructions - Each function should have a single responsibility - Extract logic into utility functions when complexity increases ### Naming Functions - Use verb-based naming that describes the action - Prefix boolean-returning functions with `is`, `has`, or `can` - Prefix void functions with action verbs like `execute`, `save`, `send` ### Reducing Nesting - Use early returns to handle edge cases first - Extract nested logic into separate functions - Employ higher-order functions (map, filter, reduce) to minimize loops - Prefer arrow functions for simple operations; use named functions otherwise ### Parameters - Use default parameters instead of null checks - When functions have multiple parameters, consolidate them into objects (RO-RO pattern) - Keep parameter lists short (max 3-4 parameters) ## Data Handling ### Data Classes - Use data classes for data structures - Encapsulate primitive types in composite types when they represent domain concepts - Validate data internally within data classes ### Immutability - Prefer immutability for data - Use `val` for variables that don't change - Use immutable collections when possible - Create new instances instead of mutating existing ones ## Classes and Objects ### Size Guidelines - Keep classes under 200 instructions - Limit to fewer than 10 public methods - Limit to fewer than 10 properties ### Design Principles - Follow SOLID principles - Favor composition over inheritance - Use interfaces for abstraction - Keep classes focused on a single responsibility ## Exception Handling ### When to Use Exceptions - Reserve exceptions for truly unexpected errors - Don't use exceptions for control flow - Catch exceptions only to: - Fix an anticipated issue - Add context before re-throwing ### Best Practices - Create custom exception types for domain-specific errors - Include meaningful error messages - Log exceptions at appropriate levels ## Testing ### Unit Tests - Follow Arrange-Act-Assert convention - Write unit tests for all public functions - Use test doubles (mocks, stubs, fakes) for dependencies - Name tests descriptively to document behavior ### Acceptance Tests - Follow Given-When-Then convention - Test user-facing behavior and scenarios - Keep tests independent and repeatable ## Code Organization - Group related functionality together - Keep files focused and cohesive - Use packages/modules to organize code by feature or layer - Maintain consistent file structure across the project
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