Can someone explain Classes?

[teraninja07064]

I really don’t get what a class is supposed to do, is it just like a container to group elements? And why do I need to define variables using @ or @@ at the beginning? Shouldn’t the scope be decided automatically depending on where I create a variable? Is there any JS equivalent to classes or is this a ruby specific concept?

[stetim94]

I really don’t get what a class is supposed to do, is it just like a container to group elements?

of sorts, i more like to think about is a blueprint. It describes something, then we create an instance you build of this blueprint/class. Sort of like a house. you make a blueprint (class) and then build the house (instance of class)

And why do I need to define variables using @ or @@ at the beginning?

A variable prefixed with @ is an instance variable, while one prefixed with @@ is a class variable. For example:

class House
 
  def initialize
    @@door = nil
    @door = nil

@door is specific for each instance (each house build from the blueprint), while @@door is shared by all instances (all houses). If we build multiple houses and we change @@door, the value changes for all instance of House class.

Shouldn’t the scope be decided automatically depending on where I create a variable?

no, look at this example:

def my_function()
  $x = 3
  y = 5
end

my_function()
puts $x
puts y

$x is global while y is local. We defined them at the same place (inside the function), yet there scope varies. So scope isn’t automatically determine by where a variable.

disclaimer: using global variable like i did above is bad practice, this is a purely demonstrative example.

@ and @@ don’t even relate to scope, its more behavioral. An instance variable is very different from a class variable.

Is there any JS equivalent to classes or is this a ruby specific concept?

OO is a concept in many language, JS has classes since es6, before there where only objects.

OO can also be found in php, python, c++ and many more.

[teraninja07064]

Isn’t it easier to use a function or a proc for that? A class can call a numer of methods or procs and do something with it. I don’t really get why it should be used instead of a normal funciton.

class Dog
  def initialize(name, breed)
    @name = name
    @breed = breed
  end
end

seems to me to be just a more complicated version of

def dog(name, breed) 
end

and the variables “name” or “breed” are automatically only accessible in a local scope when defining them as parameters of a function, so why do I need to re-define them with @?

[stetim94]

Isn’t it easier to use a function or a proc for that? A class can call a numer of methods or procs and do something with it. I don’t really get why it should be used instead of a normal funciton.

yea, it is. But i was more focusing on explaining classes.

and the variables “name” or “breed” are automatically only accessible in a local scope when defining them as parameters of a function, so why do I need to re-define them with @?

to access these properties (@name and @breed) in other methods of your class.