Block syntax (do..end and curly braces) in Ruby

Introduction

Blocks let you group code to run later or multiple times. They make your code cleaner and easier to reuse.

When you want to repeat actions for each item in a list.

When you want to run some code only inside a method call.

When you want to pass a small piece of code to another method.

When you want to organize your code clearly without making a new method.

Syntax

Ruby

method_name do
  # code here
end

# or

method_name { # code here }

Use do..end for multi-line blocks.

Use curly braces { } for single-line blocks.

Examples

This prints "Hello" three times using do..end block.

Ruby

3.times do
  puts "Hello"
end

This does the same as above but uses curly braces for a single-line block.

Ruby

3.times { puts "Hi" }

This goes through each number and prints double its value using do..end.

Ruby

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

Same as above but with curly braces for a short block.

Ruby

numbers.each { |n| puts n * 2 }

Sample Program

This program counts from 1 to 5 using a do..end block and then prints fruit names in uppercase using a curly braces block.

Ruby

5.times do |i|
  puts "Count: #{i + 1}"
end

["apple", "banana", "cherry"].each { |fruit| puts fruit.upcase }

Important Notes

Blocks are anonymous chunks of code you can pass to methods.

Curly braces have higher precedence than do..end, so use them carefully in complex expressions.

Blocks can take parameters inside pipes | | to use values from the method.

Summary

Blocks group code to run inside methods.

Use do..end for multi-line blocks and { } for single-line blocks.

Blocks can take parameters to work with data from the method.

Practice

1. Which block syntax is generally preferred for multi-line blocks in Ruby?

easy

A. Both are equally preferred for multi-line blocks

B. { }

C. Neither; Ruby does not support blocks

D. do..end

Solution

1. Step 1: Understand block syntax options

   Ruby supports two block syntaxes: do..end and curly braces { }.

2. Step 2: Identify usage for multi-line blocks

   do..end is preferred for multi-line blocks because it improves readability.

3. Final Answer:

   do..end -> Option D

4. Quick Check:

   Multi-line blocks use do..end [OK]

Hint: Use do..end for multi-line blocks, braces for single-line [OK]

Common Mistakes:

• Using curly braces for multi-line blocks reduces readability
• Thinking Ruby doesn't support blocks
• Believing both syntaxes are identical in all cases

2. Which of the following is the correct syntax for a single-line block that prints each number in an array?

easy

A. [1, 2, 3].each { |n| puts n }

B. [1, 2, 3].each { n puts | }

C. [1, 2, 3].each (|n| puts n )

D. [1, 2, 3].each do |n| puts n

Solution

1. Step 1: Identify correct block syntax for single-line

   Single-line blocks use curly braces { } with parameters inside pipes | |.

2. Step 2: Check syntax correctness

   [1, 2, 3].each { |n| puts n } correctly uses { |n| puts n }. Others have syntax errors.

3. Final Answer:

   [1, 2, 3].each { |n| puts n } -> Option A

4. Quick Check:

   Single-line block with braces and pipes [OK]

Hint: Use { |var| ... } for single-line blocks [OK]

Common Mistakes:

• Missing pipes around block parameters
• Using do..end without proper line breaks
• Incorrect placement of pipes or braces

3. What is the output of the following Ruby code?

(1..3).map { |x| x * 2 }

medium

A. [1, 2, 3]

B. [2, 4, 6]

C. [3, 6, 9]

D. SyntaxError

Solution

1. Step 1: Understand the range and map method

   The range (1..3) produces numbers 1, 2, 3. The map method applies the block to each number.

2. Step 2: Calculate each mapped value

   Each number is multiplied by 2, resulting in 2, 4, and 6.

3. Final Answer:

   [2, 4, 6] -> Option B

4. Quick Check:

   Map doubles each element [OK]

Hint: map applies block to each element and returns new array [OK]

Common Mistakes:

• Confusing map with each (which returns original array)
• Expecting a syntax error due to block syntax
• Misunderstanding range behavior

4. Identify the error in this Ruby code:

5.times do |i| puts i }

medium

A. Missing closing end for the block

B. Missing block parameter pipes | |

C. Incorrect use of curly brace to close a do..end block

D. No error, code runs fine

Solution

1. Step 1: Check block opening and closing syntax

   The block starts with do but incorrectly ends with a curly brace }.

2. Step 2: Understand correct block closure

   Blocks opened with do must close with end, not }.

3. Final Answer:

   Incorrect use of curly brace to close a do..end block -> Option C

4. Quick Check:

   do..end blocks cannot close with braces [OK]

Hint: Match do with end, braces with braces [OK]

Common Mistakes:

• Mixing do..end with curly braces
• Forgetting to close the block
• Misplacing block parameter pipes

5. Given the array [1, 2, 3, 4], which block syntax correctly filters even numbers and returns them as a new array?

hard

A. [1, 2, 3, 4].select { |n| n.even? }

B. [1, 2, 3, 4].select do |n| n.even?

C. [1, 2, 3, 4].select { n.even? }

D. [1, 2, 3, 4].select do n.even? end

Solution

1. Step 1: Understand the select method and block parameters

   select filters elements for which the block returns true. The block must receive each element as a parameter.

2. Step 2: Check syntax correctness

   [1, 2, 3, 4].select { |n| n.even? } correctly uses curly braces with block parameter |n| and calls n.even?. [1, 2, 3, 4].select do |n| n.even? has a syntax error (missing end). [1, 2, 3, 4].select { n.even? } misses block parameters. [1, 2, 3, 4].select do n.even? end misses pipes around parameter.

3. Final Answer:

   [1, 2, 3, 4].select { |n| n.even? } -> Option A

4. Quick Check:

   Curly braces with pipes for single-line filter [OK]

Hint: Use { |var| condition } for concise filtering blocks [OK]

Common Mistakes:

• Omitting block parameters
• Mixing do..end without pipes for parameters
• Using incorrect block syntax causing errors