Block parameters in Ruby

Introduction

Block parameters let you give names to values passed into a block. This helps you use those values inside the block easily.

When you want to work with each item in a list inside a block.

When you want to pass values from a method to a block and use them.

When you want to write reusable code that works with different inputs.

When you want to make your code clearer by naming the values inside a block.

Syntax

Ruby

collection.each do |parameter1, parameter2|
  # code using parameter1 and parameter2
end

Block parameters go between vertical bars | | right after do or {.

You can have one or more parameters separated by commas.

Examples

This example uses one block parameter num to double each number.

Ruby

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

This example uses two block parameters number and word to access each pair's elements.

Ruby

pairs = [[1, 'one'], [2, 'two']]
pairs.each do |number, word|
  puts "#{number} means #{word}"
end

Sample Program

This program prints a sentence for each fruit using a block parameter named fruit.

Ruby

fruits = ['apple', 'banana', 'cherry']
fruits.each do |fruit|
  puts "I like #{fruit}s"
end

Important Notes

If you forget block parameters, you can't access the values inside the block.

You can use either do |params| ... end or curly braces { |params| ... } for blocks.

Summary

Block parameters name the values passed into a block.

They go inside | | after do or {.

Use them to work with each item or value inside the block.

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