What will I learn from Metaprogramming Ruby?

Question

Will I learn anything in Metaprogramming Ruby that is not covered in any of: Programming Ruby, The Ruby Cookbook, The Ruby Programming Language or The Ruby Way, all of which have at least a chapter's material covering metaprogramming in Ruby?

It also has about a third of the book devoted to Rails, which I'm not particularly interested in reading about. Is it worth buying considering I have the above books?

EDIT: One thing that I am particulary interested in seeing is new applications of metaprogramming to solve problems. It helps fill in the gaps in my knowledge and feeds my imagination in finding different ways to look at problems themselves.

Answer 1

A book about metaprogramming should be a book about when to not metaprogram; it's one of the most overused concepts these days.

Compare

%w(flush_all version quit).each { |cmd|
  class_eval do
    define_method "#{cmd}" do
      book_it(cmd.to_sym)
      send_to_peer "#{cmd}\r\n"
    end
  end
}

to

def flush_all; send_command(:flush_all) end
def version;   send_command(:version)   end
def quit;      send_command(:quit)      end

def send_command(cmd)
  book_it(cmd)
  send_to_peer "#{cmd}\r\n"
end

(Taken from http://ozmm.org/posts/define_method_and_rdoc.html)

Metaprogramming can make sense, but it can also mess up your code. This probably didn't answer your question, but it's something worth being aware of anyway.

Answer 2

Disclaimer: I'm strongly biased when it comes to Metaprogramming Ruby, because I'm the author of the book.

The books you already mentioned don't leave many metaprogramming stones unturned. However, I think you'll still enjoy Metaprogramming Ruby. Try downloading the book samples from http://www.pragprog.com/titles/ppmetr (especially the first pages of the "Methods" chapter and the "Spell Book"). If you like those, you'll probably like the rest of the book.

The part of the book that focus on Rails is way shorter than one third - just about 40 pages. It just looks at the Rails source for examples of metaprogramming, so you don't really have to be interested in Rails to read it.