Instance variable

Use single @.

class Foo
  def initialize(my_foo)
    @my_foo = my_foo
  end

  def bar
    puts @my_foo
  end
end

f = Foo.new(12)
f.bar
# 12

Method calls

Call a method within a method using self.

class Foo
  def foo
    puts 'Hello'
  end

  def bar
    self.foo
  end
end

f = Foo.new
f.bar

Static class variable

Use double @.

class Foo
  @@FOO = 'abc'

  def bar
    puts @@FOO
  end
end

Attributes

Getter

You need a getter otherwise the variable is not available outside the instance.

class Foo
  def initialize(protein)
    @protein = protein
  end

  def protein
    @protein
  end

  def protein=(value)
    @protein = value
  end
end

foo = Foo.new(21)

# Getter
foo.protein
# 21

# Setter
foo.protein = 100

Attribute accessor

See guide - How to Use attr_accessor, attr_writer & attr_reader and Ruby OOP.

Shorthand for the getter and setter.

class Foo
  attr_accessor :protein

  def initialize(protein)
    @protein = protein
  end
end

There are three kinds:

  • attr_accessor - read and write
  • attr_reader - read only
  • attr_writer - write only

Using a colon.

class Foo
  attr_accessor :protein

  def initialize(foo, bar, protein:)
    @protein = protein
  end
end

If you use attr_accessor :protein you can do sets/gets on the field @protein automatically.

api = Foo.new(debug: true)

puts api.debug
# true

api.debug = false
puts api.debug
# false

That is similar to Python:

def initialize(foo, bar, **, debug=None):