From: Robert Klemme <shortcutter@...>
Date: 2009-09-01T22:52:04+09:00
Subject: Easy Proxy

Hi,

it just occurred to me that one sometimes might want to use a proxy
for an instance variable which restricts access in some way.

class Proc
  def proxy(meth)
    class<<self;self;end.send(:alias_method, meth, :call)
    self
  end
end

class X
  def initialize
    @e = []
  end

  def entries
    en = lambda {|x| @e << x if x >= 0; en}.proxy(:<<)
  end
end

x = X.new
x.entries << 10 << -12 << 23
p x

You can even use it for things like this:

NULL = lambda {|y| y == 0}.proxy :===
POS = lambda {|y| y > 0}.proxy :===
NEG = lambda {|y| y < 0}.proxy :===

(-2..2).each do |i|
  case i
  when NEG
    puts "#{i} NEG"
  when NULL
    puts "#{i} NULL"
  when POS
    puts "#{i} POS"
  else
    puts "#{i} what?"
  end
end

Anybody think this should go into the core?  (I'm not religious about the name.)

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/