Kotlin

1. Basic syntax

   Packages, functions, val vs var, string templates, conditionals, loops, ranges.

2. Basic types

   Numbers, Boolean, Char, String, arrays, type conversions.

3. Control flow

   if and when expressions, for/while loops, break/continue and returns.

4. Functions

   Named and default arguments, varargs, single-expression functions, infix, tail recursion.

5. Lambdas and higher-order functions

   Function types, lambda expressions, closures, trailing lambdas and function references.

6. Inline functions

   inline, noinline, crossinline and reified type parameters.

7. Null safety

   Nullable types, safe calls, Elvis operator, not-null assertion and smart casts.

8. Classes and objects

   Constructors, properties, init blocks, visibility modifiers, nested classes and inheritance.

9. Interfaces and inheritance

   Interfaces, abstract and open classes, overriding rules and property overrides.

10. Data, sealed and enum classes

    Data classes, copy and destructuring, sealed classes and interfaces, enum classes.

11. Objects and companions

    Singleton objects, companion objects and object expressions.

12. Extensions

    Extension functions and properties and how they resolve statically.

13. Scope functions

    let, run, with, apply and also, and choosing among them.

14. Generics

    Type parameters, variance (in/out), declaration-site variance, type projections, constraints.

15. Delegation and delegated properties

    Class delegation with by, lazy, observable and custom delegated properties.

16. Collections

    List, Set, Map, mutable vs read-only, sequences, and collection operations.

17. Exceptions

    try/catch/finally as expressions, throw, no checked exceptions, Nothing type.

18. Operator overloading and DSLs

    Conventions for operators, invoke, and building type-safe builders.

19. Coroutines

    suspend functions, launch/async, structured concurrency, dispatchers, cancellation and exceptions.

20. Flow and channels

    Cold asynchronous streams, flow operators, StateFlow, SharedFlow and channels.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.

Source: endoflife.date