Design Principles in the Functional World

Daniel Leon

Optymyze

[25th of October 2014]

Motivation

Question list

1) Design patterns vs design principles2) Anything else besides design type?3) How about functional principles?

Principle vs patternPrinciple Pattern

Rules Concrete examples

Language/paradigm independent Language/paradigm dependent

Generic diagrams Class UML

Types of programming principles1) Design principles

Single responsibilityOpen/closedLiskov substitutionInterface segregationDependency inversion

2) Packaging principlesCohesionCoupling

Object-oriented principlesSingle Responsibility Principle -  A class should have one, and only one, reason to change.

Open-Closed Principle - You should be able to extend a classes behavior, without modifying it.

Liskov Substitution Principle - Derived classes must be substitutable for their base classes.

Interface Segregation Principle – Make fine grained interfaces that are client specific.

Dependency Injection Principle - Depend on abstractions, not on concretions.

Functional principles ?Single Responsibility Principle -  A function should have one, and only one, reason to change.

Open-Closed Principle - You should be able to extend a function behavior, without modifying it.

Liskov Substitution Principle - Derived functions must be substitutable for their base functions.

Interface Segregation Principle – Make fine grained traits that are client specific.

Dependency Injection Principle - Depend on traits, not on concretions.

Creational design patterns

Factory

Lazy initialization

Singleton

Structural design patterns

Adapter

Decorator

Behavioral design patterns

Chain of responsibility

Command

Command

Dependency inversion

Null object

Strategy

Conclusions

• Patterns are to principles what are implementations to patterns

• Sometimes to much design patterns in code shows the lack of design principles implementation in the language

• Java 8 still has some work to do in order to catch-up Scala

My reaction to Java 8

Bibliographyhttp://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

http://www.objectmentor.com/resources/articles/Principles_and_Patterns.pdf

http://java.dzone.com/articles/design-patterns-decorator http://pavelfatin.com/design-patterns-in-scala

Design Principles in the Functional WorldDaniel Leon[Optymyze]

[25th of October 2014]

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