Practice Exercises 2

Let's think this through for a second

This lesson is tougher than Exercises 1, combining OOP class design, blocks/yield, and Hash data structures into tasks that mix things together. It's a chance to practice the class-object, initialize, getters-setters, and blocks concepts from the Advanced chapter in something close to a real-world scenario. Work through the tasks in order and you'll build up practice step by step, from class design all the way to block-based iteration.

Exercises

Task 1: Build a Book class with title and author attributes using attr_accessor and initialize. Task 2: Build a Library class with an add_book(book) method that adds Book objects to a @books array — then write a find_by_author(name) method that uses a .select block to return the list of books matching the given author name. Task 3: Write a word_frequency(text) method that uses Hash.new(0) to count how many times each word appears in a sentence. Task 4: Write a yield_even_numbers(numbers) { |n| ... } method that yields each even number in the array to the block passed in by the caller.

Built the Book and Library classes using attr_accessor, an array, and a block (select)
Wrote the word_frequency method's word-count logic using Hash.new(0)
Wrote the yield_even_numbers method so it works with a custom block using the yield keyword

Code Example

ruby

class Book
  attr_accessor :title, :author

  def initialize(title, author)
    @title = title
    @author = author
  end
end

class Library
  def initialize
    @books = []
  end

  def add_book(book)
    @books << book
  end

  def find_by_author(name)
    # TODO: block/select သုံးပြီး author name နဲ့ ကိုက်ညီတဲ့ book တွေကို ပြန်ပေးပါ
  end
end

def word_frequency(text)
  # TODO: Hash.new(0) သုံးပြီး word တစ်လုံးချင်းစီရဲ့ အကြိမ်ရေကို ရေတွက်ပါ
end

def yield_even_numbers(numbers)
  # TODO: block ကိုသုံးပြီး even number တစ်ခုချင်းစီအတွက် yield ပေးပါ
end

library = Library.new
library.add_book(Book.new("Ruby Basics", "Matz"))
p library.find_by_author("Matz")
p word_frequency("ruby is fun and ruby is easy")
yield_even_numbers([1, 2, 3, 4, 5, 6]) { |n| puts n }

You should see

find_by_author should return a list of Book objects, word_frequency should return a Hash like {"ruby"=>2, "is"=>2, ...}, and yield_even_numbers should print numbers like 2, 4, 6 with puts.

5-Minute Challenge

Write a new find_by_title(keyword) method on the Library class that uses a .select block to return books whose title contains the keyword — try it in 5 minutes.

One Quick Warning

Checking block_given? before using yield in a method makes your error handling better — keep this pattern in mind when writing production code.