Rails - May 2006 - class_eval in ROR''s attribure_accessor.rb

hi,
here is a snippet code in ROR''s attribure_accessor.rb. the usage of 
class_eval is different  with "class_eval(string, <, file,
<line>>)"
somewhat,
i don''t understand this usage, who can explain it more detail to me?

  def cattr_writer(*syms)
    syms.flatten.each do |sym|
      class_eval(<<-EOS, __FILE__, __LINE__)
        unless defined? @@#{sym}
          @@#{sym} = nil
        end

        def self.#{sym}=(obj)
          @@#{sym} = obj
        end

        def #{sym}=(obj)
          @@#{sym} = obj
        end
      EOS
    end
  end

can  it write as fellow:

  def cattr_writer(*syms)
    syms.flatten.each do |sym|
      class_eval(<<-EOS
        unless defined? @@#{sym}
          @@#{sym} = nil
        end

        def self.#{sym}=(obj)
          @@#{sym} = obj
        end

        def #{sym}=(obj)
          @@#{sym} = obj
        end
      EOS, __FILE__, __LINE__)
    end
  end

-- 
Posted via http://www.ruby-forum.com/.

On May 4, 2006, at 11:12 PM, mengjiang liu wrote:
> here is a snippet code in ROR''s attribure_accessor.rb. the usage
of
> class_eval is different  with "class_eval(string, <, file,
<line>>)"
> somewhat,
> i don''t understand this usage, who can explain it more detail to
me?
 From the Ruby documentation for Module#class_eval: "The optional  
_filename_ and _lineno_ parameters set the text for error messages."

$ ri class_eval

jeremy