Block parameters in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are block parameters in Ruby?

Block parameters are variables that a block receives when it is called. They allow the block to accept input values and use them inside the block.

beginner

How do you define block parameters in Ruby?

Block parameters are defined between vertical bars | | right after the block keyword or do. For example: array.each { |item| puts item } where item is the block parameter.

beginner

What happens if you don't specify block parameters in a Ruby block?

If you don't specify block parameters, the block will not receive any input values from the method calling it. You won't be able to access the values passed to the block.

intermediate

Can a Ruby block have multiple parameters? How?

Yes, a Ruby block can have multiple parameters separated by commas inside the vertical bars. For example: array.each_with_index { |item, index| puts "#{index}: #{item}" } where item and index are block parameters.

intermediate

What is the difference between block parameters and method parameters in Ruby?

Block parameters are variables passed to a block, which is a chunk of code passed to a method. Method parameters are variables passed to the method itself. Blocks are called inside methods and can receive their own parameters separately.

How do you write block parameters in Ruby?

A Inside square brackets [ ] after the block keyword

B Inside parentheses ( ) after the method name

C Inside curly braces { } after the method name

D Inside vertical bars | | after the block keyword

Block parameters are always written inside vertical bars | | right after the block keyword or do.

What will this code print?
[1, 2, 3].each { |n| puts n * 2 }

A 2 4 6

B 1 2 3

C nil

D Error

The block parameter n takes each element, multiplies by 2, and prints it.

What happens if you omit block parameters but the block expects them?

A The block will ignore the passed values

B The block will receive default values

C The block will raise an error

D The block will run normally without parameters

If no block parameters are specified, the block ignores any values passed to it.

Which of these is a valid block parameter list?

A {item, index}

B |item, index|

C (item, index)

D [item, index]

Block parameters are always inside vertical bars | | separated by commas.

Can a block parameter be named the same as a method parameter?

A Only if the method is private

B No, it causes a syntax error

C Yes, they are in different scopes

D Only if the block is empty

Block parameters and method parameters have separate scopes, so they can have the same name without conflict.

Explain what block parameters are and how you use them in Ruby.

Think about how a block receives values from a method like each.

Describe the difference between method parameters and block parameters in Ruby.

Consider how methods and blocks receive their inputs separately.

Practice

1.

What are block parameters in Ruby?

Choose the best description.

easy

A. Variables inside | | that receive values passed to the block.

B. Methods that define how a block works.

C. Special keywords to start a block.

D. Constants used only outside blocks.

Solution

1. Step 1: Understand block parameters role

   Block parameters are variables placed inside | | after do or { to receive values passed into the block.

2. Step 2: Compare options with definition

   Only Variables inside | | that receive values passed to the block. correctly describes block parameters as variables inside | | that get values passed to the block.

3. Final Answer:

   Variables inside | | that receive values passed to the block. -> Option A

4. Quick Check:

   Block parameters = variables inside | | [OK]

Hint: Block parameters are always inside | | after do or { [OK]

Common Mistakes:

• Confusing block parameters with methods
• Thinking block parameters are keywords
• Assuming block parameters are constants

2.

Which of the following is the correct syntax for block parameters in Ruby?

array.each do ?

easy

A. [item] puts item

B. (item) puts item

C. |item| puts item

D. {item} puts item

Solution

1. Step 1: Recall block parameter syntax

   Block parameters are placed inside vertical bars | | after do or {.

2. Step 2: Match syntax with options

   Only |item| puts item uses |item| which is the correct syntax for block parameters.

3. Final Answer:

   |item| puts item -> Option C

4. Quick Check:

   Block parameters use | | [OK]

Hint: Block parameters always go inside | | after do or { [OK]

Common Mistakes:

• Using parentheses () instead of | |
• Using curly braces {} for parameters
• Using square brackets [] for parameters

3.

What is the output of this Ruby code?

numbers = [1, 2, 3]
numbers.each do |n|
  puts n * 2
end

medium

A. 2
4
6

B. 1
2
3

C. Error: undefined variable n

D. nil

Solution

1. Step 1: Understand the block parameter usage

   The block parameter n takes each element from the array numbers one by one.

2. Step 2: Calculate output for each element

   For each n, the code prints n * 2. So outputs are 2, 4, and 6 on separate lines.

3. Final Answer:

   2 4 6 -> Option A

4. Quick Check:

   Each number doubled = 2,4,6 [OK]

Hint: Block parameter holds each item; multiply inside block [OK]

Common Mistakes:

• Confusing block parameter with array variable
• Expecting original numbers printed
• Thinking block parameter is undefined

4.

Find the error in this Ruby code:

fruits = ['apple', 'banana']
fruits.each do fruit|
  puts fruit
end

medium

A. Block parameter should be in parentheses

B. Missing closing | after block parameter

C. No error, code runs fine

D. Missing opening | before block parameter

Solution

1. Step 1: Check block parameter syntax

   Block parameters must be enclosed inside vertical bars | |. Here, only the closing bar is present.

2. Step 2: Identify missing part

   The opening | before fruit is missing, causing a syntax error.

3. Final Answer:

   Missing opening | before block parameter -> Option D

4. Quick Check:

   Block parameters need both | | [OK]

Hint: Block parameters always need both | at start and end [OK]

Common Mistakes:

• Forgetting the opening |
• Using parentheses instead of | |
• Assuming code runs without |

5.

Given this code, what will be the output?

pairs = [[1, 2], [3, 4], [5, 6]]
pairs.each do |a, b|
  puts a + b
end

hard

A. [1, 2]
[3, 4]
[5, 6]

B. 3
7
11

C. Error: wrong number of block parameters

D. 1
3
5

Solution

1. Step 1: Understand multiple block parameters

   The block parameters a and b receive each inner array's two elements separately.

2. Step 2: Calculate sum for each pair

   For each pair, the code prints the sum: 1+2=3, 3+4=7, 5+6=11.

3. Final Answer:

   3 7 11 -> Option B

4. Quick Check:

   Sum of pairs = 3,7,11 [OK]

Hint: Use multiple block parameters to unpack arrays inside each [OK]

Common Mistakes:

• Expecting array printed instead of sum
• Thinking block parameters can't unpack arrays
• Assuming syntax error with two parameters