Constants in classes in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing a constant inside a nested class

What is the output of this Ruby code?

Ruby

class Outer
  CONST = 10
  class Inner
    CONST = 20
    def self.show
      CONST
    end
  end
end

puts Outer::Inner.show

A nil

B 10

C 20

D NameError

💡 Hint

Remember that constants inside a nested class override outer constants with the same name.

The Inner class defines its own CONST as 20, so Outer::Inner.show returns 20.

❓ Predict Output

intermediate

Accessing a constant from an outer class

What will this Ruby code print?

Ruby

class A
  VALUE = 5
  class B
    def self.get_value
      A::VALUE
    end
  end
end

puts A::B.get_value

A 0

B nil

C NameError

D 5

💡 Hint

Use the scope resolution operator to access constants from outer classes.

A::VALUE is 5, so A::B.get_value returns 5.

❓ Predict Output

advanced

Constant lookup with inheritance and nesting

What is the output of this Ruby code?

Ruby

class Parent
  CONST = 'parent'
end

class Child < Parent
  CONST = 'child'
  class Nested
    def self.value
      CONST
    end
  end
end

puts Child::Nested.value

A NameError

B nil

C "parent"

D "child"

💡 Hint

Constants inside nested classes do not inherit from the outer class or its ancestors automatically.

Nested class does not have CONST defined and does not inherit from Child, so CONST is undefined and raises NameError.

❓ Predict Output

advanced

Constant resolution with explicit scope

What does this Ruby code print?

Ruby

module M
  CONST = 100
  class C
    CONST = 200
    def self.show
      M::CONST
    end
  end
end

puts M::C.show

A 200

B 100

C NameError

D nil

💡 Hint

Using M::CONST accesses the constant defined in the module M, not the class C.

M::CONST is 100, so M::C.show returns 100.

🧠 Conceptual

expert

Behavior of constant reassignment in Ruby classes

Consider this Ruby code snippet. What will be the output and why? class X CONST = 1 CONST = 2 def self.value CONST end end puts X.value

A Warning and 2

B 1

C 2

D Error

💡 Hint

Ruby allows constant reassignment but warns about it.

Ruby prints a warning about constant reassignment but the value is updated to 2, so output is 2 with a warning.