Lambda creation and behavior in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple lambda call

What is the output of this Ruby code?

Ruby

my_lambda = ->(x) { x * 3 }
puts my_lambda.call(4)

A 4

B 12

C Error: wrong number of arguments

D nil

💡 Hint

Remember that the lambda multiplies the input by 3.

The lambda takes one argument x and returns x multiplied by 3. Calling it with 4 returns 12.

❓ Predict Output

intermediate

Lambda argument count enforcement

What happens when this Ruby code runs?

Ruby

my_lambda = ->(x, y) { x + y }
puts my_lambda.call(5)

A 5 + nil (TypeError)

B 5

C nil

D Error: wrong number of arguments (given 1, expected 2)

💡 Hint

Lambdas check the number of arguments strictly.

The lambda expects 2 arguments but only 1 is given, so Ruby raises an ArgumentError.

❓ Predict Output

advanced

Difference between lambda and proc in argument handling

What is the output of this Ruby code?

Ruby

my_proc = Proc.new { |x, y| x.to_i + (y || 0) }
my_lambda = ->(x, y) { x + y }
puts my_proc.call(5)
puts my_lambda.call(5)

A

5
5

B

Error
Error

C

5
Error: wrong number of arguments (given 1, expected 2)

D

nil
Error

💡 Hint

Procs are lenient with arguments, lambdas are strict.

The proc treats missing arguments as nil and uses default 0, so 5 + 0 = 5. The lambda requires exactly 2 arguments and raises an error when only 1 is given.

🧠 Conceptual

advanced

Return behavior inside lambda vs proc

What happens when this Ruby code runs?

Ruby

def test_lambda
  l = -> { return "from lambda" }
  l.call
  "after lambda"
end

def test_proc
  p = Proc.new { return "from proc" }
  p.call
  "after proc"
end

puts test_lambda
puts test_proc

A

after lambda
from proc

B

after lambda
after proc

C

from lambda
after proc

D

from lambda
from proc

💡 Hint

Return inside a proc exits the method, return inside a lambda exits only the lambda.

The lambda's return exits only the lambda block, so the method continues and returns 'after lambda'. The proc's return exits the whole method immediately, returning 'from proc'.

🔧 Debug

expert

Why does this lambda raise an error?

This Ruby code raises an error. Which option explains the cause?

Ruby

my_lambda = ->(x) { x + y }
y = 10
puts my_lambda.call(5)

A NameError because y is not defined inside the lambda's scope at the time of call

B ArgumentError because lambda expects 2 arguments but only 1 given

C SyntaxError due to missing parentheses in lambda definition

D No error, outputs 15

💡 Hint

Check variable scope inside lambdas.

The variable y is defined after the lambda is created, but the lambda captures the environment at creation. Since y is not in scope inside the lambda when called, a NameError is raised.