Method lookup chain in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the method defined in the class.

Ruby

class Animal
  def speak
    'Hello'
  end
end

animal = Animal.new
puts animal.[1]

Drag options to blanks, or click blank then click option'

Aspeak

Brun

Cjump

Dtalk

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call a method that does not exist in the class.

Using a wrong method name.

The method speak is defined in the Animal class. Calling animal.speak runs that method and prints 'Hello'.

2fill in blank

medium

Complete the code to call the method from the module included in the class.

Ruby

module Talk
  def speak
    'Hi from module'
  end
end

class Person
  include Talk
end

p = Person.new
puts p.[1]

Drag options to blanks, or click blank then click option'

Arun

Bspeak

Cjump

Dtalk

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a method not defined in the module or class.

Confusing module methods with class methods.

The Person class includes the Talk module, which defines the speak method. So calling p.speak uses the module's method.

3fill in blank

hard

Fix the error by completing the code to call the method from the superclass.

Ruby

class Vehicle
  def start
    'Starting engine'
  end
end

class Car < Vehicle
end

car = Car.new
puts car.[1]

Drag options to blanks, or click blank then click option'

Adrive

Bpark

Cstop

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call a method not defined in the class or its ancestors.

Using a method name that does not exist.

The Car class inherits from Vehicle. The start method is defined in Vehicle, so car.start calls that method.

4fill in blank

hard

Fill both blanks to complete the method lookup chain with module and superclass methods.

Ruby

module M
  def greet
    'Hello from M'
  end
end

class A
  def greet
    'Hello from A'
  end
end

class B < A
  include M
end

b = B.new
puts b.[1]
puts b.class.superclass.instance_method(:[2]).bind(b).call if b.class.superclass.method_defined?(:[2])

Drag options to blanks, or click blank then click option'

Agreet

Bstart

Crun

Dspeak

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names for the two blanks.

Not matching the method name in the superclass call.

The object b calls greet from module M first. Then it calls greet from its superclass A using b.class.superclass.instance_method(:greet).bind(b).call.

5fill in blank

hard

Fill all three blanks to complete the method lookup chain with class, module, and superclass methods.

Ruby

module M1
  def action
    'Action from M1'
  end
end

module M2
  def action
    'Action from M2'
  end
end

class Parent
  def action
    'Action from Parent'
  end
end

class Child < Parent
  include M1
  include M2

  def action
    'Action from Child'
  end
end

c = Child.new
puts c.[1]
puts c.singleton_class.ancestors[2].instance_method(:action).bind(c).call
puts c.class.superclass.instance_method(:[2]).bind(c).call if c.class.superclass.method_defined?(:[3])

Drag options to blanks, or click blank then click option'

Aaction

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names for blanks.

Confusing the order of method lookup.

The Child class defines action, which is called first. Then the method from the last included module M2 is called via singleton_class.ancestors[2]. Finally, the action method from the superclass Parent is called.