Question

I would like to initialize several auto-vivifying hashes by one-line expression. So far I came to an extra method for the AutoHash object:

class AutoHash < Hash
  ...
  def few(n=0)
    Array.new(n) { AutoHash.new }
  end

which allows me to do the following

a, b, c = AutoHash.new.few 3

However, I feel that one can make the following sentence possible by defining a new operator :=

a := b := c = AutoHash.new

Could you help me to implement this?

---

Do I have to use superators?

require 'superators'

class AutoHash < Hash
  ...
  superator ":=" do |operand|
    if operand.kind_of? Hash
      ...
    else
      ...
    end
  end

---

Update: Now I see that the operator needs to be defined outside the class. Is it possible to define such object clone operator?

---

Update2 More clear definition of method few, thanks to Joshua

---

References

1. http://www.linux-mag.com/cache/7432/1.html
2. Does Ruby support var references like PHP?
3. http://ruby.about.com/od/advancedruby/a/deepcopy.htm

Answer 1

Where you ask for a := b := c := AutoHash.new.few 3 I think (not sure I understand your desire) that you really want a,b,c=Autohash.new.few 3

---

Why does few take variable args, when you only ever use the first?

I also find your creation of the return value to be confusing, maybe try

def few(n=0) 
  Array.new(n) { AutoHash.new } 
end 

---

Beyond that, it seems like few should be a class method. a,b,c=AutoHash.few 3 which will work if you defined few on the class:

def AutoHash.few(n=0)
  Array.new(n) { AutoHash.new }
end

---

If a,b,c=AutoHash.few 3 isn’t what you’re looking for, and you really want to implement your own operator, then check out Hacking parse.y, which was a talk given at RubyConf 2009. You can watch the presentation at http://rubyconf2009.confreaks.com/19-nov-2009-17-15-hacking-parsey-tatsuhiro-ujihisa.html and you can see the slides at http://www.slideshare.net/ujihisa/hacking-parsey-rubyconf-2009