Printing variables - ruby

Question

My problem is probably quite easy, but I couldn't find an answer anywhere.
When create a class, for example:
class Book
#author = "blabla"
#title = "blabla"
#number_of_pages"
I want to create a method to print out my variables. And here I'm getting a problem when I try:
def Print
puts #author, #title, #number_of_pages
end
I am getting nothing.
When I try:
def Print
puts "#author, #title, #number_of_pages"
end
I get straight: "#author, #title, #number_of_pages"
How can I make the Print method print out the variables' values?

Answer 1

You should move your variable initializations to initialize:
class Book
def initialize
#author = "blabla"
#title = "blabla"
#number_of_pages = 42 # You had a typo here...
end
end
The way you have it in your question, the variables are class instance variables (which you can Google if you're curious about, but it's not really relevant here).
Initialized as (normal) instance variables, your first version of Print() works if you're just looking to dump the state -- it prints each parameter on its own line.
To make your second version of Print() work, you need to wrap your variables in #{} to get them interpolated:
def print # It's better not to capitalize your method names
puts "#{#author}, #{#title}, #{#number_of_pages}"
end

Answer 2

In addition to the allready exellent answer of Darshan, here is the way you would do it optimally
class Book
attr_accessor :author, :title, :number_of_pages
#so that you can easily read and change the values afterward
def initialize author, title, number_of_pages = nil
#so that you don't really need to provide the number of pages
#author = author
#title = title
#number_of_pages = number_of_pages
end
def print
puts "#{#author}, #{#title}, #{#number_of_pages}"
end
end
my_book = Book.new("blabla", "blabla", 42)
my_book.title = "this is a better title"
my_book.print
#=>blabla, this is a better title, 42

Answer 3

I think Darshan Computing has already solved your problem very well. But here I would like to give you alternative ways of achieving that.
I assume that you'd like to print out all the instance variables you have in the class. The method instance_variables could return an array of all your instance_variables in symbols. And then you can iterate them do whatever you want. Please be careful: instance_variable_get is pretty convenient but not the best practice.
class Book
attr_reader :author, :title, :number_of_pages
def initialize(author, title, number_of_pages)
#author = author
#title = title
#number_of_pages = number_of_pages
end
def print_iv(&block)
self.instance_variables.each do |iv|
name = iv
value = send(iv.to_s.gsub(/^#/, ''))
# value = instance_variable_get(iv) # Not recommended, because instance_variable_get is really powerful, which doesn't actually need attr_reader
block.call(name, value) if block_given?
end
end
end
rb = Book.new("Dave Thomas", "Programming Ruby - The Pragmatic Programmers' Guide", 864)
# rb.instance_variables #=> [:#author, :#title, :#number_of_pages]
rb.print_iv do |name, value|
puts "#{name} = #{value}"
end
#=> #author = Dave Thomas
#=> #title = Programming Ruby - The Pragmatic Programmers' Guide
#=> #number_of_pages = 864
# You can also try instance_eval to run block in object context (current class set to that object)
# rb.instance_eval do
# puts author
# puts title
# puts number_of_pages
# end