class - ruby: Trouble understanding classes and defining variables with @ -

i doing rspec tutorial , having difficulties reading tests. current test trying read is:

 describe book    before     @book = book.new   end    describe 'title'     'should capitalize first letter'       @book.title = "inferno"       @book.title.should == "inferno"     end 

i can understand asking me do: create class book , method inside class capitalize. thoughts on how code wrong (i have seen example of code works in case)

what tried do:

class book     def initialize(book)         @book = book     end      def title(@book)         @book.capitalize     end end 

solution ended working:

class book      attr_reader :title      def initialize(title=nil)       @title = title && title.capitalize!     end      def title=(new_title)         @title = new_title && new_title.capitalize!     end end 

i not understand @ does. thought create variable works throughout entire class. in addition, wondering why @title used instead of @book (which specified in rspec test).

in addition, struggling "before do" part of code , why asks @book = book.new

also part && confusing well. why not ok put @title = title.capitalize!

i happy clarify of if not make sense (i know post long).

the @ fundamental construct in ruby: instance variable class. don't have pass param within methods of class. it's known entire instance of class. see, example, instance variables , accessors details.

so following isn't valid since don't pass instance variables method parameters:

def title(@book)     @book.capitalize end 

the && go second statement if first true or not nil. example

def initialize(title=nil)   @title = title && title.capitalize! end 

will set class' instance variable @title parameter title.capitalize! long title isn't nil. if title nil, @title set title (i.e., nil). if class created without parameter, @title set nil , error won't generated calling nil method capitalize!.