About attr_accessor

What is an instance variable?

Variables shared inside the same instance

`python`


class Food
  def initialize(name)
    #Save the name passed when creating the instance in the instance variable
　  @name = name
  end

  def eat
　　"I will eat an #{@name}"
  end
end
food = Food.new('apple')
food.hello #=> "I will eat an apple"

Instance variables cannot be referenced from outside the class!

`python`


class Food
  def initialize(name)
　  @name = name
  end

  #@Method for referencing name from the outside
  def name
　　@name
  end
end
food = Food.new('apple')
#Via the name method@Get the contents of name
food.name #=> "apple"

If you want to change the contents of an instance variable from the outside, define a method for changing

`python`


class Food
  def initialize(name)
　  @name = name
  end

  #@Method for referencing name from the outside
  def name
　　@name
  end

　#@Method for changing name from the outside
  def name=(value)
    @name = value
  end
end
food = Food.new('apple')
#It looks like you're assigning it to a variable, but it's actually a name=You are calling a method.
food.name = 'banana'
#Via the name method@Get the contents of name
food.name #=> "banana"

A method that reads and writes the value of an instance variable is called an "accessor method". Writing these methods one by one is a hassle. That's where the "attr_accessor method" comes in.

attr_accessor method

`python`


class Food
  #@Methods to read and write name are automatically defined
  attr_accessor :name

  def initialize(name)
　  @name = name
  end

  #@Method for referencing name from the outside
  #def name
　　#@name
  #end

　#@Method for changing name from the outside
  #def name=(value)
    #@name = value
  #end
end
food = Food.new('apple')
#@Change name
food.name = 'banana'
#@Refer to name
food.name #=> "banana"

"Attr_reader" if you want to make the contents of the instance variable read-only If you want to write only, "attr_writer"

reference An introduction to Ruby for those who want to become professionals