java15-design-patterns-made-functional-workshop

• references
  • OOP v̶s̶ and FP by Mario Fusco
  • g ∘ f patterns by Mario Fusco
  • https://github.com/mariofusco/from-gof-to-lambda
  • https://en.wikipedia.org/wiki/First-class_citizen
  • https://en.wikipedia.org/wiki/First-class_function
  • https://www.quora.com/What-is-a-Single-Abstract-Method-SAM-interface-in-Java-8

preface

• to refresh knowledge about design patterns please refer: https://github.com/mtumilowicz/designPatterns
• goals of this workshop
  • show some design patterns in a more functional way
  • introduction to basic functional programming structures enabling neat design
    • functions as a first-class citizen
    • streams
• workshops: /lambda/<Name>Workshop
• answers: /lambda/<Name>

introduction

• Single Abstract Method (SAM) type
  • another name for @FunctionalInterfaces
    • functional interface is also known as Single Abstract Method Interface
  • example: Runnable, Callable, etc
  • provide target types for lambda expressions and method references
• first-class citizen
  • is an entity which supports all the operations generally available to other entities
  • operations typically include being passed as an argument, returned from a function, modified, and assigned to a variable
• programming language is said to have first-class functions if it treats functions as first-class citizens

mapping

Pattern	Lambda
Chain of Responsibility	Stream of functions
Decorator	Functions composition
Interpreter	Map of functions
Iterator	Stream
Strategy	SAM
Template	SAM
Visitor	Map of functions

• note that many more patterns from GOF could be rewritten in a more functional way by simply using SAM conversion
  • example: Observer