Challenge 2: Custom to_s — Solution

class Book
  attr_accessor :title, :author, :pages

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

  def to_s
    "'#{@title}' by #{@author} (#{@pages} pp.)"
  end
end

book = Book.new("The Hobbit", "J.R.R. Tolkien", 310)
puts book

=begin
Output:
'The Hobbit' by J.R.R. Tolkien (310 pp.)

Notes:
- to_s is defined like any other instance method, but Ruby treats it
  specially: puts (and string interpolation, and many other places) calls
  to_s automatically any time it needs to turn an object into a string.
- puts book works with no explicit book.to_s call — that's the whole
  point of overriding to_s instead of writing a separate describe method
  and remembering to call it everywhere.
- Without this override, puts book would have printed Ruby's default,
  unhelpful representation, something like #<Book:0x00007f... >.
=end