Proc creation and call in Ruby - Mini Project: Build & Apply

Proc creation and call

📖 Scenario: Imagine you are building a simple calculator that can perform different operations. You want to use Ruby's Proc objects to store these operations and call them when needed.

🎯 Goal: Create a Proc that adds two numbers, store it in a variable, and then call it to get the result.

📋 What You'll Learn

Create a Proc that takes two numbers and returns their sum.

Store the Proc in a variable called add_proc.

Call the add_proc with the numbers 5 and 7.

Print the result of the Proc call.

💡 Why This Matters

🌍 Real World

Procs let you store blocks of code to reuse later, like saving a recipe to cook anytime.

💼 Career

Understanding Procs helps in Ruby programming for flexible and reusable code, common in web development and automation.

1

Create a Proc that adds two numbers

Create a Proc called add_proc that takes two parameters a and b and returns their sum.

Ruby

# Create a Proc called add_proc that adds two numbers
# Your code here

Hint

Use Proc.new { |a, b| a + b } to create the Proc.

2

Call the Proc with two numbers

Call the add_proc with the numbers 5 and 7 and store the result in a variable called result.

Ruby

add_proc = Proc.new { |a, b| a + b }
# Call add_proc with 5 and 7 and store in result
# Your code here

Hint

Use add_proc.call(5, 7) to call the Proc.

3

Print the result

Print the value of the variable result using puts.

Ruby

add_proc = Proc.new { |a, b| a + b }
result = add_proc.call(5, 7)
# Print the result
# Your code here

Hint

Use puts result to print the sum.

4

Use the Proc with different numbers

Call the add_proc with the numbers 10 and 15 and print the result directly using puts.

Ruby

add_proc = Proc.new { |a, b| a + b }
result = add_proc.call(5, 7)
puts result
# Call add_proc with 10 and 15 and print the result
# Your code here

Hint

Use puts add_proc.call(10, 15) to print the new sum.

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