Class_eval and instance_eval in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a method to the class using class_eval.

Ruby

class MyClass
  class_eval do
    def greet
      puts [1]
    end
  end
end

obj = MyClass.new
obj.greet

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

AHello from class_eval!

B"Hello from instance_eval!"

C"Hello from class_eval!"

Dputs "Hello"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string.

Using instance_eval instead of class_eval here.

The string must be quoted to be printed correctly. Using class_eval adds the method to the class.

2fill in blank

medium

Complete the code to define an instance variable using instance_eval.

Ruby

class MyClass
  def initialize
    @name = "Ruby"
  end
end

obj = MyClass.new
obj.instance_eval do
  @name = [1]
end

puts obj.instance_eval { @name }

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

AChanged by instance_eval

Bname

C:Changed

D"Changed by instance_eval"

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning a string without quotes.

Trying to access @name without instance_eval.

The instance variable @name is set to a string, so it must be quoted.

3fill in blank

hard

Fix the error in the code by completing the blank to call instance_eval correctly.

Ruby

class MyClass
  def initialize
    @value = 10
  end
end

obj = MyClass.new
result = obj.[1] { @value * 2 }
puts result

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

Ainstance_eval

Bself_eval

Ceval

Dclass_eval

Attempts:

3 left

💡 Hint

Common Mistakes

Using class_eval instead of instance_eval.

Using eval which is a Kernel method, not related to the object.

instance_eval runs the block in the context of the object, allowing access to @value.

4fill in blank

hard

Fill both blanks to add a class method using class_eval and call it.

Ruby

class MyClass
  [1].class_eval do
    def self.say_hello
      "Hello from class method"
    end
  end
end

puts MyClass.[2]

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

Aself

Binstance

Csay_hello

Dgreet

Attempts:

3 left

💡 Hint

Common Mistakes

Calling class_eval on an instance.

Calling a method that does not exist.

class_eval is called on the class object, and the method say_hello is called on MyClass.

5fill in blank

hard

Fill all three blanks to define an instance variable with instance_eval, define a method with class_eval, and call both.

Ruby

class MyClass
  [1].class_eval do
    def greet
      "Hello, #{@name}!"
    end
  end
end

obj = MyClass.new
obj.[2] do
  @name = [3]
end

puts obj.greet

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

Aself

Binstance_eval

C"Ruby Learner"

Dclass_eval

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up class_eval and instance_eval calls.

Not quoting the string for @name.

class_eval is called on the class to define the method. instance_eval is called on the object to set @name. The name must be a string.