Paradigm shift - from behaviours inside object in OOAD to Julia where behaviours emerge from type of function parameters...

OOAD Thought Processing

    Concept → Owner

• Behavior → Object
• Polymorphism → Virtual methods
• Extension → Subclassing
• Encapsulation → Methods inside class

Julia Thought Processing

    Concept → Owner

• Behavior → Generic function
• Polymorphism → Multiple dispatch
• Extension → Add new methods
• Encapsulation → Types + modules

OO Design Thinking

• Identify entities (classes)
• Attach behavior to them
• Use inheritance for variation

Julia Design Thinking

• Identify operations (functions)
• Define data types
• Implement methods for combinations of types

Worldview Comparison

OOP worldview

The world is made of interacting objects.

Julia worldview

The world is made of operations applied to data.

The State Pattern in Pure Julia Style

Enjoy the State pattern written in Julia.

Note that this works without the context class of the original State Pattern, which is typically implemented using object-oriented languages like C++, Java, or Python.

abstract type ChickenState end

struct Uncleaned <: ChickenState end

struct Washed <: ChickenState end

struct Marinated <: ChickenState end

struct Cooked <: ChickenState end

function wash(::Uncleaned)

println("Chicken is getting cleaned → Washed")

sleep(2)

return Washed()

end

wash(s::ChickenState) = s # default: no change

function marinate(::Washed)

println("Chicken is being marinated → Marinated")

sleep(2)

return Marinated()

end

marinate(s::ChickenState) = s

function cook(::Marinated)

println("Chicken is being cooked → Cooked")

sleep(4)

return Cooked()

end

cook(s::ChickenState) = s

function serve(::Cooked)

println("Chicken is being served. Final state.")

return Cooked()

end

serve(s::ChickenState) = s

state = Uncleaned()

state = wash(state)

state = marinate(state)

state = cook(state)

state = serve(state)

Here's the Python implementation of the State Design Pattern.

Feel the difference - Pythonian way and the Julian way.