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GeekNight 22.0 Multi-paradigm programming in Scala and Akka
- 1.
- 2. Why not both? Youreally don’t have to choose just one.
- 3. Agenda for tonight ⊸Demonstrate a blend of OOP and FP in a hybrid language - Scala ⊸ Use Scala with Akka to easily build scalable Actor Systems
- 4. ⊸ Disclaimer: ▫ Thisis not a talk about Scala as a language, its features or its comparison with Java. Don’t want to do this => ▫ As polyglot programmers, we acknowledge that some languages are better than others for the specific kind of problems that they are trying to solve. ▫ Scala and Java are just being used as tools to understand and help in embracing functional programming paradigm.
- 5. ➢ Why shouldyou consider another programming paradigm?
- 6. ➢ What isthe Best code?
- 7. ➢ What isthe Best code? ○ The following =>
- 8. ➢ What isthe Best code? ○ The best code is the one that doesn't exists! Why? ○ Code rots. ○ needs maintenance. ○ needs to be tested. ○ needs to be read and understood again and again over time. Conciseness matters!
- 10. ➢ Get allproducts from the orders
- 11. ➢ Get allproducts from the orders Or
- 12. ➢ Sort theproducts by Id Or
- 13. ➢ Why Scala? ○Because Scala smoothens the transition from OOP to FP. ○ Supplements Java and adds more features and reduces the verbosity. ○ It is not new - first introduced in 2003.
- 14. ➢ Why learnFunctional Programming ?
- 15. ➢ Why learnFunctional Programming ? ○ Write high-performing code that's easier to understand and reason about. ○ Write programs that can utilize multiple cores more efficiently. ○ It would evolve your way of thinking about programs and eventually make you a better programmer.
- 16. ➢ How doesFP improve code?
- 17. ➢ How doesFP improve code? ○ Scalable and efficient code that can utilize multiple cores better - Map/Reduce engines. ○ Better to reason about code. No need to create mental model or remember gradual state changes. ○ By emphasizing on the evaluation of expressions instead of evaluation of statements
- 18. ➢ What isfunctional programming ? ○ Immutability. ○ Referential transparency. ○ Higher order functions. ○ Tail call recursion, mapping, reducing, currying, lazy evaluation,...
- 19. ➢ What isfunctional programming ? ○ Immutability. ○ Referential transparency. ○ Higher order functions. ○ Tail call recursion, mapping, reducing, currying, lazy evaluation,... ➢ Writing code without side effects. It is a restriction on how we write programs and not on what programs we can express.
- 20. ➢ What makesScala functional ?
- 21. ➢ Functions are1st class citizens => ○ Instead =>
- 22. ➢ Functions are1st class citizens => ○ Instead =>
- 23. ➢ Immutability (preferred) ○Preventing reference reassignment through val. ○ Avoiding mutable state through immutable collections. ■ Eg : 2 threads referring to same tree.
- 24. ➢ After onethread adds a node. ○ Immutability has benefits in concurrency as synchronization is not needed.
- 25. ➢ Having referentialtransparency. ○ Should hold substitution model. ➢ No side effects
- 26. ➢ Having referentialtransparency. ○ Should hold substitution model. ➢ No side effects StringBuilder.append has side effects!
- 28. String is referentiallytransparent and holds substitution model.
- 29. ➢ Similarly, add() hereis also without side-effects and referentially transparent.
- 30. ➢ Function withSide Effect ○ A function has side effects if it does something other than simply return a result like ■ Modifying a variable/data structure. ■ Throwing exception or halting abruptly. ■ Reading/writing to file/database ■ … ➢ In a pure function ○ Input is obtained only by parameters. ○ Output is calculated and returned.
- 31. ➢ Just enoughScala for Akka.
- 32. ➢ Case classes ○Regular classes which export their constructor parameters and which provide a recursive decomposition mechanism via pattern matching. ○ The params can be accessed with .(dot) notation.
- 33. ➢ Pattern matching ○Switch case on steroids
- 34. ➢ Pattern matching ○A pattern match includes a sequence of alternatives, each starting with the keyword ‘case’. ○ Each alternative case includes a pattern and one or more expressions, which will be evaluated if the pattern matches. ○ An arrow symbol => separates the pattern from the expressions. Example =>
- 35.
- 38.
- 39. The Actor Model ⊸Avoiding shared mutable state ▫ Functional Programming - all state is immutable ▫ Actor Model - state is mutable but encapsulated in actors
- 40. What’s an actor? ⊸An actor has state ⊸ An actor has behaviour ⊸ …. Sounds similar to something else, doesn’t it?
- 41. Actors are what“objects” were supposed to be ⊸ Actors are what objects are supposed to be (Smalltalk objects) ⊸
- 42. What’s an actor? ⊸An actor has state ⊸ An actor has behaviour Similar to OOP objects but with one difference ⊸ Actors communicate by sending immutable messages to each other
- 43. Akka - actorson the JVM ⊸ Akka actors ▫ are light-weight JVM objects ▫ are guaranteed to run on a single thread (no locks/synchronization required) ▫ process messages sent to them in order and one at a time ▫ do not share their state ▫ can be addressed irrespective of location ▫ asynchronous and non-blocking
- 44. What is Akka? Akkais a toolkit and runtime for building highly concurrent, distributed, and resilient message-driven applications on the JVM.
- 45. Anatomy of anactor An akka actor must have ⊸ State ⊸ Behavior ▫ Message processing
- 46.
- 47.
- 48. Let’s look atan actor
- 49.
- 50. Scaling out inclusters ⊸ Location transparency with ActorRef ⊸ Akka’s cluster and cluster-sharding modules ⊸ Resilience with Supervision strategies
- 51. Where to gofrom here ⊸ Take Martin Odersky’s course on Coursera ⊸ Try out some Lightbend Activator projects from Github ⊸ Reach out the Akka team on Gitter and Google Groups
- 52. Start thinking inHybrids
- 53.