Explanation of attr_* in Ruby.

attr.rb

# Explanation of attr_* to Noxn

# Let's start with an example class using attr_acessor:
class Klass
  attr_acessor :variable

  def initialize(content)
    @variable = content
  end
end

klass = Klass.new("Variable's content")
# So now, Klass̈́' instance variable called "variable"'s (@variable)
# value is the string "Variable's content"
# attr_acessor defined two methods (shown later),
# it allows us to "access" the variable in two ways,
# one being to change the value:
klass.variable = "New content"

# Other one being retrieving the value:
klass.variable
#=> "New content"


# As I said before, attr_acessor simply is a shortcut for two methods:
class Klass
  def initialize(content)
    @variable = content
  end

  def variable=(content)
    @variable = content
  end

  def variable
    @variable
  end
end

# But because these are so common tasks, the shortcut is provided.
# There is also:
# attr_reader (read only)
# 
# And
# attr_writer (write only)

# So attr_acessor is just a method, it could be written like this:

def attr_acessor(*instance_variables)
  instance_variables.each do |instance_variable|
    define_method(instance_variable) do
      self.instance_variable_get(instance_variable)
    end

    define_method(instance_variable + "=") do |new_value|
      self.instance_variable_set(instance_variable, new_value)
    end
  end
end

# And with that method, it would be pretty easy to write attr_writer and
# attr_reader, of course :) (And attr_acessor should actually just call these
# methods, but we do it like this for the sake of example)