From: 7stud -- <bbxx789_05ss@...>
Date: 2009-03-31T12:50:27+09:00
Subject: Re: When to use instance variables @

Steve Dogers wrote:
> Hi, I have a couple questions about instance variables in Ruby.
> 1) do i need to declare them at the top of my class file - I do
> understand the accessors are automatic 

Then you're understanding is faulty:

class Person

  def initialize(name, age)
    @name = name
    @age = age
  end

end


p = Person.new("Steve", 25)
puts p.name

--output:--
undefined method `name' for #<Person:0x2529c @age=25, @name="Steve"> 
(NoMethodError)




> but I'm not sure if I can just
> pull a @product in the middle of a function
> 

They are called "methods" in ruby.

class Person

  def initialize(name, age)
    @name = name
    @age = age
  end

  def somefunc(x)
    @product = x
  end

  def show
    puts "I have #{@product}"
  end

end

p = Person.new("Steve", 25)
p.somefunc("Shoes")
p.show

--output:--
I have Shoes


> 2) do i need to use the @ to refer to them in the class. Would it work
> without the @, 

class Person
  def initialize(name, age)
    @name = name
    @age = age
  end

  def somefunc(x)
    @product = x
  end

  def show
    puts "I have #{product}"  #<-- no @
  end

end


p = Person.new("Steve", 25)
p.somefunc("Shoes")
p.show

--output:--
in show undefined local variable or method `product' for 
#<Person:0x24ef0 @age=25, @product="Shoes", @name="Steve"> (NameError)


> and if so, how does it differentiate them from local
> vars?
> 

class Person

  def initialize(name, age)
    @name = name
    @age = age
  end

  def somefunc(x)
    @product = x
  end

  def show
    product = "Sandals"
    puts "I have #{product}"
    puts "I have #{@product}"
  end

end


p = Person.new("Steve", 25)
p.somefunc("Shoes")
p.show

--output:--
I have Sandals
I have Shoes



> 3) I've seen code where just below the class declaration, objects are
> instantiated like product = Product.new - I don't see a @ sign, does
> that mean it's a local var? How can a local var even exist at the class
> level, outside a function?
> 

class Product
  def initialize
    @product = "Shoes"
  end
end

class Person
  product = Product.new

  def initialize(name, age)
    @name = name
    @age = age
  end

  def show
    #puts product
    #puts @product
    #puts @@product
    puts Person.product
  end

end


p = Person.new("Steve", 25)
p.show


--output:--
in `show': undefined method `product' for Person:Class (NoMethodError)
        from r3test.rb:24

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