Let us quickly go over Ruby objects. In the real world, objects may be anything including a car, computer, or even a human. Each one of these objects have different states and behaviors.
An object in Ruby has very similar characteristics. Ruby Objects also have states and behaviors. In Ruby Objects, the state is stored in instance variables and the behaviors are stored in `methods` (functions within classes).
A class is basically an object's template. This template defines the available `properties` that make up the object using `instance variables`. Again, there are also `behaviors` defined in the form of `methods` to help change the object's state.
A new instance of a class is created using the `initialize` method of a class. An instance will have properties required to initialize the instance as dictated by the class' initialize method.
As you saw, classes are defined using the `class` keyword and the class code block ends with an `end` keywork. The `initialize` method is the constructor which is a special function to describe initial state. When we create this object, we define the attributes `@make`, `@model`, and `@color` with values we pass into the constructor.
Yay, we just created a `mazda3` which is an instance of the `Car` object. This is great, but sometimes you may need to change some of these attributes! Most of these attributes in this example would be static. Still, imagine that you decided to get a new paintjob. How would you go about updating the state of this `mazda3`?
Thankfully, it is rather simple to update the state of an object. First, we would need a `setter` method! Ruby defines **getter** and **setter** settings as the `attr_reader` and `attr_accessor` respectively. For both getter and setter settings on a given attribute, you can also just use `attr_accessor`.
To demonstrate this, I have modified the previous Car object with these newly defined settings.
Viewing the previous output from [`irb`](https://en.wikipedia.org/wiki/Interactive_Ruby_Shell), you can see that each one of the instance variables is readable. We can write to `@color`, but we end up causing a `NoMethodError` exception when we attempt to write to `@make`. This is because `@make` was only defined using an `attr_reader`, so `make=` is not defined. This could be fixed by adding the make to the `attr_accessor` like we did for color.
Lets say that a class is created, which contains an array that we would like to access directly. For instance, say our class `Car` had an array of nicknames that we wanted to know.
```Ruby
class Car
attr_accessor :color
attr_reader :make, :model, :nicknames
def initialize(make, model, color, nicknames)
@make = make
@model = model
@color = color
@nicknames = nicknames
end
def turn(direction)
end
def honk
puts "beep beep"
end
def brake
end
end
```
We can assign the car an array of nicknames and access them by calling the `attr_reader` for `nicknames`
```Ruby
c = Car.new("Volvo","V70", "Black", ["The Wagon","Long Fella","Slick"])
Sometimes, we may not want to have to reference a specific variable, or the return type is implied by the object. In this case, it would be handy to call the car object and directly reference `nicknames`. With ruby we can overload methods such as `[]` like so
```Ruby
class Car
attr_accessor :color
attr_reader :make, :model, :nicknames
def initialize(make, model, color, nicknames)
@make = make
@model = model
@color = color
@nicknames = nicknames
end
def [](key)
@nicknames[key]
end
def []=(key,value)
@nicknames[key] = value
end
def turn(direction)
end
def honk
puts "beep beep"
end
def brake
end
end
```
Here, we have added two methods, `[]` and `[]=`. These methods are special because they allow us to index the `Car` object directly, in this case to resolve a nickname. Here's an example of how we can use these methods
```Ruby
irb(main):030:0> c = Car.new("Volvo","V70", "Black", ["The Wagon","Long Fella","Slick"])
- [Ruby Class Relationships Explained Through Pokemon](https://medium.com/@tpstar/object-relationships-in-ruby-explained-by-relationships-in-pokemons-8dd64c8af773)
