Nil as the absence of value in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Understanding nil in conditional expressions

What is the output of this Ruby code snippet?

Ruby

value = nil
if value
  puts "Value is true"
else
  puts "Value is false or nil"
end

A Value is true

B nil

C Value is false or nil

D Error: undefined variable

💡 Hint

Remember that in Ruby, only false and nil are treated as false in conditionals.

In Ruby, nil is treated as false in conditionals, so the else branch runs.

❓ Predict Output

intermediate

Nil and method calls

What happens when you call a method on nil in Ruby?

Ruby

result = nil.to_s
puts result

A nil

B "" (empty string)

C NoMethodError

D false

💡 Hint

Check what methods nil supports in Ruby.

Calling to_s on nil returns an empty string "".

❓ Predict Output

advanced

Nil in array operations

What is the output of this Ruby code?

Ruby

arr = [1, nil, 3]
filtered = arr.compact
puts filtered.inspect

A [1, 3]

B Error: undefined method 'compact'

C [nil]

D [1, nil, 3]

💡 Hint

The compact method removes nil elements from arrays.

The compact method returns a new array without any nil values.

❓ Predict Output

advanced

Nil and equality checks

What is the output of this Ruby code?

Ruby

a = nil
b = false
puts a == b
puts a.nil?
puts b.nil?

A

false
true
false

B

true
true
true

C

false
false
false

D

true
false
true

💡 Hint

Check how nil compares to false and how the nil? method works.

nil == false is false because they are different objects.
nil.nil? is true because it is nil.
false.nil? is false because false is not nil.

🧠 Conceptual

expert

Nil and safe navigation operator

What is the output of this Ruby code using the safe navigation operator (&.)?

Ruby

person = nil
name = person&.name
puts name.nil?

A NoMethodError

B false

C nil

D true

💡 Hint

The safe navigation operator prevents errors when calling methods on nil.

The safe navigation operator &. returns nil instead of raising an error if the object is nil.
So name is nil, and name.nil? returns true.