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Enumerator & Enumerable Mastery

Enumerators are powerful Ruby objects that provide lazy evaluation, custom iteration, and chaining capabilities. They're essential for memory-efficient processing, infinite sequences, and creating custom iterators. Master the Enumerable module and custom enumerators.

Enumerator Basics & Creation

Enumerators: Enumerators are objects that provide iteration capabilities with lazy evaluation. They allow you to create custom iterators, chain operations, and process data efficiently without loading everything into memory.

Creating Enumerators

# Creating enumerators from existing objects
array = [1, 2, 3, 4, 5]
enum = array.each
puts
enum.class
# Enumerator

# Using Enumerator.new with a block
fib_enum = Enumerator.new do |yielder|
  a, b = 0, 1
  loop
do
    yielder << a
    a, b = b, a + b
  end
end

puts
fib_enum.take(10)
# [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

# Using to_enum method
range_enum = (1..10).to_enum
puts
range_enum.next
# 1
puts
range_enum.next
# 2

Key Feature: Enumerators provide lazy evaluation, meaning they only compute values when needed. This makes them perfect for infinite sequences and memory-efficient processing.

Lazy Evaluation & Infinite Sequences

Lazy Enumerators

# Lazy evaluation with large datasets
numbers = (1..1_000_000).lazy
result = numbers
  .select(&:even?)
  .map { |x| x * x }
  .take(5)

puts
result.to_a
# [4, 16, 36, 64, 100]

# Infinite sequence example
infinite_squares = Enumerator.new do |yielder|
  n = 1
  loop
do
    yielder << n * n
    n += 1
  end
end

puts
infinite_squares.take(10)
# [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Custom Infinite Sequences

# Prime numbers enumerator
primes = Enumerator.new do |yielder|
  n = 2
  loop
do
    if (2..Math.sqrt(n)).none? { |i| n % i == 0 }
      yielder << n
    end
    n += 1
  end
end

puts
primes.take(10)
# [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]

# Random numbers enumerator
random_numbers = Enumerator.new do |yielder|
  loop
do
    yielder << rand(1..100)
  end
end

puts
random_numbers.take(5)
# [42, 17, 89, 3, 56] (random)

Enumerable Module & Custom Iterators

Making Classes Enumerable

# Custom enumerable class
class
NumberRange
  include Enumerable
  
  def initialize(start, stop, step = 1)
    @start = start
    @stop = stop
    @step = step
  end
  
  def each
    current = @start
    while
current <= @stop
      yield current
      current += @step
    end
  end
end

range = NumberRange.new(1, 10, 2)
puts
range.to_a
# [1, 3, 5, 7, 9]
puts
range.sum
# 25
puts
range.select(&:odd?)
# [1, 3, 5, 7, 9]

Enumerator Methods

# Enumerator control methods
enum = (1..5).each

# Manual iteration
puts
enum.next
# 1
puts
enum.next
# 2
puts
enum.peek
# 3 (doesn't advance)
puts
enum.next
# 3

# Rewind to beginning
enum.rewind
puts
enum.next
# 1

# Check if enumeration is finished
enum = (1..3).each
enum.next; enum.next; enum.next
puts
enum.next
# raises StopIteration

Interactive Practice: Enumerator & Enumerable

Practice Time: Try these enumerator and enumerable examples and experiment with different lazy evaluation patterns. Understanding these concepts will make you a more effective Ruby programmer.

Interactive Code Runner

Ruby Code Editor

# Try these comprehensive enumerator examples!

# 1. Basic enumerator creation
array = [1, 2, 3, 4, 5]
enum = array.each
puts "Enumerator class: #{enum.class}"
puts "First element: #{enum.next}"
puts "Second element: #{enum.next}"

# 2. Fibonacci sequence enumerator
fib_enum = Enumerator.new do |yielder|
  a, b = 0, 1
  loop do
    yielder << a
    a, b = b, a + b
  end
end

puts "\nFibonacci sequence (first 10):"
puts fib_enum.take(10)

# 3. Lazy evaluation with large datasets
numbers = (1..1_000_000).lazy
result = numbers
  .select(&:even?)
  .map { |x| x * x }
  .take(5)

puts "\nLazy evaluation result:"
puts result.to_a

# 4. Infinite sequence - squares
infinite_squares = Enumerator.new do |yielder|
  n = 1
  loop do
    yielder << n * n
    n += 1
  end
end

puts "\nInfinite squares (first 10):"
puts infinite_squares.take(10)

# 5. Prime numbers enumerator
primes = Enumerator.new do |yielder|
  n = 2
  loop do
    if (2..Math.sqrt(n)).none? { |i| n % i == 0 }
      yielder << n
    end
    n += 1
  end
end

puts "\nPrime numbers (first 10):"
puts primes.take(10)

# 6. Custom enumerable class
class NumberRange
  include Enumerable
  
  def initialize(start, stop, step = 1)
    @start = start
    @stop = stop
    @step = step
  end
  
  def each
    current = @start
    while current <= @stop
      yield current
      current += @step
    end
  end
end

range = NumberRange.new(1, 10, 2)
puts "\nCustom NumberRange:"
puts "to_a: #{range.to_a}"
puts "sum: #{range.sum}"
puts "select odd: #{range.select(&:odd?)}"
puts "map squares: #{range.map { |x| x * x }}"

# 7. Enumerator control methods
enum = (1..5).each
puts "\nEnumerator control:"
puts "next: #{enum.next}"
puts "next: #{enum.next}"
puts "peek: #{enum.peek}"  # doesn't advance
puts "next: #{enum.next}"

enum.rewind
puts "After rewind, next: #{enum.next}"

# 8. Random numbers enumerator
random_numbers = Enumerator.new do |yielder|
  loop do
    yielder << rand(1..100)
  end
end

puts "\nRandom numbers (first 5):"
puts random_numbers.take(5)

# 9. File line enumerator
# Create a temporary file for demonstration
require 'tempfile'

temp_file = Tempfile.new('demo')
temp_file.write("Line 1\nLine 2\nLine 3\nLine 4\nLine 5")
temp_file.close

file_enum = File.foreach(temp_file.path)
puts "\nFile lines:"
file_enum.each { |line| puts line.strip }

temp_file.unlink

# 10. Chaining enumerators
numbers = (1..20).lazy
result = numbers
  .select { |n| n % 2 == 0 }
  .map { |n| n * n }
  .select { |n| n > 50 }
  .take(3)

puts "\nChained operations:"
puts "Even numbers squared > 50 (first 3): #{result.to_a}"

# Add your own enumerator experiments below!

Output will appear here when you run the code...

Enumerator & Enumerable Best Practices

✅ Do This

Use lazy enumerators for large datasets
Create custom enumerators for infinite sequences
Include Enumerable in custom classes
Use take() to limit infinite sequences
Chain operations for efficient processing

❌ Avoid This

Forgetting to use lazy for large datasets
Creating infinite loops without take()
Not handling StopIteration exceptions
Using enumerators when arrays are simpler
Ignoring memory implications

Enumerator & Enumerable Mastery Checklist

Enumerator Creation: Create enumerators from existing objects and with blocks
Lazy Evaluation: Use lazy enumerators for memory-efficient processing
Infinite Sequences: Create enumerators for infinite data streams
Enumerable Module: Include Enumerable in custom classes
Manual Control: Use next, peek, and rewind for manual iteration
Chaining: Chain enumerator operations for complex processing
Error Handling: Handle StopIteration exceptions properly
Performance: Understand when to use lazy vs eager evaluation

Next Steps: Practice with enumerators for infinite sequences, lazy evaluation, and custom iterators. Enumerators are essential for memory-efficient processing and powerful iteration patterns!

Enumerator & Enumerable Mastery

Enumerator & Enumerable Mastery

Enumerator Basics & Creation

Creating Enumerators

Lazy Evaluation & Infinite Sequences

Lazy Enumerators

Custom Infinite Sequences

Enumerable Module & Custom Iterators

Making Classes Enumerable

Enumerator Methods

Interactive Practice: Enumerator & Enumerable

Interactive Code Runner

Ruby Code Editor

Enumerator & Enumerable Best Practices

✅ Do This

❌ Avoid This

Enumerator & Enumerable Mastery Checklist

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Ruby Language

Rails Framework

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Enumerator & Enumerable Mastery

Enumerator & Enumerable Mastery

Enumerator Basics & Creation

Creating Enumerators

Lazy Evaluation & Infinite Sequences

Lazy Enumerators

Custom Infinite Sequences

Enumerable Module & Custom Iterators

Making Classes Enumerable

Enumerator Methods

Interactive Practice: Enumerator & Enumerable

Interactive Code Runner

Ruby Code Editor

Enumerator & Enumerable Best Practices

✅ Do This

❌ Avoid This

Enumerator & Enumerable Mastery Checklist

Quick Navigation

Related Topics

Video Tutorial