Proc creation and call in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Proc that returns 'Hello'.

Ruby

greet = Proc.new { [1] }

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

Areturn "Hello"

Bputs "Hello"

C"Hello"

Dprint "Hello"

Attempts:

3 left

💡 Hint

Common Mistakes

Using puts or print inside the Proc returns nil instead of the string.

Using return inside a Proc block causes an error.

The Proc should return the string "Hello". Using just the string "Hello" inside the block returns it.

2fill in blank

medium

Complete the code to call the Proc and print its result.

Ruby

greet = Proc.new { "Hello" }
puts [1]

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

Agreet.call()

Bgreet()

Cgreet.call

Dgreet

Attempts:

3 left

💡 Hint

Common Mistakes

Using just the Proc variable name prints the Proc object, not its result.

Using greet() without call is invalid syntax for Proc.

To call a Proc in Ruby, use call(). This executes the Proc and returns its value.

3fill in blank

hard

Fix the error in the code to correctly create and call a Proc that adds 5 to a number.

Ruby

add_five = Proc.new { |num| num [1] 5 }
result = add_five.call(10)
puts result

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication changes the intended result.

Using division causes unexpected results or errors.

The Proc should add 5 to the input number, so the plus operator + is correct.

4fill in blank

hard

Fill both blanks to create a Proc that checks if a number is even and call it with 8.

Ruby

is_even = Proc.new { |n| n [1] 2 == 0 }
puts is_even.[2](8)

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

A%

Bcall

C==

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using == inside the block incorrectly.

Trying to call the Proc without call method.

The modulo operator % checks the remainder when dividing by 2. The Proc is called using call.

5fill in blank

hard

Fill all three blanks to create a Proc that multiplies a number by 3, call it with 7, and print the result.

Ruby

triple = Proc.new { |x| x [1] 3 }
result = triple.[2]([3])
puts result

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

A*

Bcall

C7

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication.

Forgetting to call the Proc with an argument.

Passing the argument incorrectly.

The Proc multiplies by 3 using *. It is called with 7 using call, and the result is printed.

Practice

1. What does a Proc in Ruby do?

easy

A. Stores a block of code to run later

B. Creates a new variable

C. Defines a class

D. Starts a loop

Solution

1. Step 1: Understand what a Proc is and match description

   A Proc is a way to save some code to run later, like a recipe you keep for cooking. Only Stores a block of code to run later describes storing code to run later, which matches what a Proc does.

2. Final Answer:

   Stores a block of code to run later -> Option A

3. Quick Check:

   Proc = stored code block [OK]

Hint: Proc saves code to run later, like a saved recipe [OK]

Common Mistakes:

• Thinking Proc creates variables
• Confusing Proc with class definition
• Assuming Proc starts loops automatically

2. Which of the following is the correct way to create a Proc in Ruby?

easy

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

B. my_proc = new Proc { |x| x * 2 }

C. my_proc = Proc.create { |x| x * 2 }

D. my_proc = Proc.call { |x| x * 2 }

Solution

1. Step 1: Recall Proc creation syntax and check options

   In Ruby, you create a Proc using Proc.new or proc with a block. Only my_proc = Proc.new { |x| x * 2 } uses the correct syntax Proc.new { |x| x * 2 }. Others use invalid methods like new Proc, Proc.create, or Proc.call.

2. Final Answer:

   my_proc = Proc.new { |x| x * 2 } -> Option A

3. Quick Check:

   Proc.new + block = correct Proc creation [OK]

Hint: Use Proc.new or proc with a block to create a Proc [OK]

Common Mistakes:

• Using 'new Proc' instead of 'Proc.new'
• Trying to call Proc.create or Proc.call to create
• Missing the block braces {}

3. What is the output of this Ruby code?

my_proc = proc { |x| x + 3 }
puts my_proc.call(4)

medium

A. 4

B. Error

C. 3

D. 7

Solution

1. Step 1: Trace the Proc definition and execution

   The Proc adds 3 to the input number: x + 3. Calling my_proc.call(4) computes 4 + 3 = 7.

2. Final Answer:

   7 -> Option D

3. Quick Check:

   4 + 3 = 7 [OK]

Hint: Proc.call runs code with given argument [OK]

Common Mistakes:

• Confusing Proc.call with Proc.new
• Forgetting to pass argument to call
• Expecting output without call

4. Identify the error in this code snippet:

my_proc = Proc.new { |x| x * 2 }
puts my_proc.call

medium

A. Proc.new syntax is incorrect

B. Missing argument when calling the Proc

C. Cannot call Proc with call method

D. Block should not have parameters

Solution

1. Step 1: Analyze Proc definition and call for errors

   The Proc expects one argument x to multiply by 2. The call is made without any argument, which causes an error because x is missing.

2. Final Answer:

   Missing argument when calling the Proc -> Option B

3. Quick Check:

   Proc needs argument when called [OK]

Hint: Always pass required arguments when calling a Proc [OK]

Common Mistakes:

• Calling Proc without required arguments
• Thinking Proc.new syntax is wrong
• Believing call method is invalid

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

def create_proc
  Proc.new { |x| x.nil? ? 'No value' : x * 10 }
end

my_proc = create_proc
puts my_proc.call(nil)
puts my_proc.call(5)

hard

A. nil\n50

B. Error\n50

C. No value\n50

D. No value\n5

Solution

1. Step 1: Analyze the Proc logic and trace both calls

   The Proc checks if x is nil; if yes, returns 'No value', else returns x * 10. Calling with nil returns 'No value'. Calling with 5 returns 5 * 10 = 50.

2. Final Answer:

   No value\n50 -> Option C

3. Quick Check:

   nil -> 'No value', 5 -> 50 [OK]

Hint: Proc can handle nil with conditional inside block [OK]

Common Mistakes:

• Expecting error when passing nil
• Forgetting ternary condition inside Proc
• Assuming multiplication by 10 applies to nil