Proc vs lambda differences (arity, return) in Ruby - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a lambda that takes one argument.

Ruby

my_lambda = [1] do |x|
  x * 2
end

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

Alambda

Bproc

CProc.new

Ddef

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'proc' instead of 'lambda' which does not enforce arity.

Using 'Proc.new' which creates a proc, not a lambda.

In Ruby, lambda creates a lambda object that checks the number of arguments (arity).

2fill in blank

medium

Complete the code to create a proc that ignores extra arguments.

Ruby

my_proc = [1] do |x|
  x + 1
end

puts my_proc.call(5, 10)

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

Alambda

Bdef

CProc.new

Dproc

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lambda' which enforces exact number of arguments.

Using 'def' which defines a method, not a proc.

Using proc creates a proc that does not enforce the number of arguments strictly.

3fill in blank

hard

Fix the error in the code by choosing the correct keyword to create a lambda.

Ruby

my_func = [1] do |x, y|
  return x + y
end

puts my_func.call(2, 3)

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

Alambda

BProc.new

Cproc

Ddef

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'proc' which causes 'return' to exit the enclosing method.

Using 'Proc.new' which behaves like 'proc'.

Only lambda treats return as returning from the lambda itself, not the enclosing method.

4fill in blank

hard

Fill both blanks to create a proc and call it with two arguments, ignoring extra ones.

Ruby

my_proc = [1] do |a, b|
  a - b
end

puts my_proc.call(10, 5, [2])

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

Aproc

Blambda

C20

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lambda' which enforces exact arguments and will raise an error.

Passing no extra argument which misses the point of ignoring extras.

Using proc allows extra arguments to be ignored. The third argument '20' is ignored.

5fill in blank

hard

Fill all three blanks to create a lambda, call it with correct arguments, and return the sum.

Ruby

my_lambda = [1] do |x, y|
  [2] x + y
end

result = my_lambda.call([3], 7)
puts result

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

Alambda

Breturn

C5

Dproc

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'proc' which treats return differently.

Omitting 'return' which still works but is less explicit.

Using lambda with return returns from the lambda itself. Calling with 5 and 7 sums to 12.

Practice

1. Which statement correctly describes the difference between a Proc and a lambda in Ruby regarding argument checking?

easy

A. Both Proc and lambda check arguments strictly.

B. Proc checks arguments strictly; lambda is lenient.

C. Neither Proc nor lambda check arguments.

D. Proc is lenient with arguments; lambda checks arguments strictly.

Solution

1. Step 1: Understand argument checking behavior

   A Proc in Ruby does not enforce the number of arguments strictly; it allows missing or extra arguments without error.

2. Step 2: Compare with lambda behavior

   A lambda behaves like a method and enforces the exact number of arguments, raising an error if the count is wrong.

3. Final Answer:

   Proc is lenient with arguments; lambda checks arguments strictly. -> Option D

4. Quick Check:

   Argument checking = Proc lenient, lambda strict [OK]

Hint: Remember: lambda acts like a method, Proc is more flexible [OK]

Common Mistakes:

• Thinking both check arguments strictly
• Confusing which one is strict
• Assuming Proc raises error on wrong args

2. Which of the following is the correct syntax to create a lambda in Ruby?

easy

A. lambda = Proc.new { |x| x * 2 }

B. lambda = proc { |x| x * 2 }

C. lambda = ->(x) { x * 2 }

D. lambda = lambda.new { |x| x * 2 }

Solution

1. Step 1: Identify lambda creation syntax

   In Ruby, lambdas can be created using the literal syntax ->(args) { block } or lambda { block }. The arrow syntax is common and concise.

2. Step 2: Check each option

   lambda = Proc.new { |x| x * 2 } creates a Proc, not a lambda. lambda = ->(x) { x * 2 } uses the correct lambda literal syntax. lambda = proc { |x| x * 2 } creates a Proc using proc. lambda = lambda.new { |x| x * 2 } is invalid syntax.

3. Final Answer:

   lambda = ->(x) { x * 2 } -> Option C

4. Quick Check:

   Lambda syntax = ->(args) { block } [OK]

Hint: Use ->(args) { } for lambda, Proc.new or proc for Proc [OK]

Common Mistakes:

• Using Proc.new when lambda is needed
• Trying lambda.new which doesn't exist
• Confusing proc and lambda syntax

3. What will be the output of the following Ruby code?

def test_proc
  p = Proc.new { return "From Proc" }
  p.call
  return "From method"
end

puts test_proc

medium

A. "From Proc"

B. "From method"

C. nil

D. RuntimeError

Solution

1. Step 1: Understand Proc return behavior

   When a Proc executes a return, it returns from the enclosing method, not just the Proc block.

2. Step 2: Trace the code execution

   Calling p.call triggers the Proc's return, which exits the test_proc method immediately with "From Proc". The later return "From method" is never reached.

3. Final Answer:

   "From Proc" -> Option A

4. Quick Check:

   Proc return exits method = "From Proc" [OK]

Hint: Proc return exits method; lambda return exits lambda only [OK]

Common Mistakes:

• Thinking return exits only the Proc block
• Expecting "From method" output
• Confusing Proc and lambda return behavior

4. Identify the error in the following Ruby code and fix it:

def test_lambda
  l = lambda { |x| return x * 2 }
  l.call
  return "Done"
end

puts test_lambda

medium

A. No error; output is "Done"

B. Error: lambda expects argument; fix by passing argument to l.call

C. SyntaxError: lambda block missing do/end

D. Error: lambda return exits method; fix by removing return inside lambda

Solution

1. Step 1: Check lambda argument requirements

   The lambda expects one argument x, but l.call is called without arguments, causing an ArgumentError.

2. Step 2: Fix the call by passing an argument

   Calling l.call(5) or any value fixes the error. The lambda returns x * 2, but this return exits only the lambda, so the method continues and returns "Done".

3. Final Answer:

   Error: lambda expects argument; fix by passing argument to l.call -> Option B

4. Quick Check:

   Lambda arity strict = pass correct args [OK]

Hint: Lambda needs exact args; always pass them when calling [OK]

Common Mistakes:

• Ignoring missing argument error
• Thinking lambda return exits method
• Assuming no arguments needed for lambda

5. Given the following code, what will be the output?

def test
  l = ->(x) { return x * 2 }
  p = Proc.new { return "Proc return" }
  result_l = l.call(3)
  result_p = p.call
  return "Method end"
end

puts test

hard

A. "Proc return"

B. "Method end"

C. 6

D. ArgumentError

Solution

1. Step 1: Execute lambda call

   The lambda l is called with argument 3, returns 6, but its return exits only the lambda, so method continues.

2. Step 2: Execute Proc call

   The Proc p is called next. Its return exits the entire method immediately with "Proc return". The later return "Method end" is never reached.

3. Final Answer:

   "Proc return" -> Option A

4. Quick Check:

   Proc return exits method, lambda return exits lambda [OK]

Hint: Proc return exits method immediately; lambda return does not [OK]

Common Mistakes:

• Expecting method to return "Method end"
• Confusing which return exits method
• Ignoring Proc's immediate method exit