From: Chuck Remes <cremes.devlist@...>
Date: 2010-10-21T00:31:20+09:00
Subject: [Q] best practice for redefining methods at runtime?

I have a class that I would like to "freeze" when it reaches a particular state so that it becomes read-only. I do *not* want to use the existing #freeze method because it raises an exception when there is an attempted mutation on a frozen object and I want the attempt to be silent. It appears that the best way to enforce this (state machine pattern) is by redefining the accessors and other methods that cause mutations to be no ops.

What is the preferred practice for doing that?

Here's an example of my approach:

class Foo
  attr_accessor :bar, :baz, :quxxo
  
  def freeze!
    do_nothing = Proc.new {|val| nil}
    recreate_method(:bar=, do_nothing)
    recreate_method(:baz=, do_nothing)
    recreate_method(:quxxo=, do_nothing)
  end
  
  private
  
  def recreate_method name, meth
    self.class.send(:define_method, name, meth)
    nil
  end
end


ruby-1.9.2-p0 > f=Foo.new
 => #<Foo:0x0000010185f7d0> 
ruby-1.9.2-p0 > f.bar=2
 => 2 
ruby-1.9.2-p0 > f.baz=9
 => 9 
ruby-1.9.2-p0 > f.freeze!
 => nil 
ruby-1.9.2-p0 > f.inspect
 => "#<Foo:0x0000010185f7d0 @bar=2, @baz=9>" 
ruby-1.9.2-p0 > f.bar=3
 => 3 
ruby-1.9.2-p0 > f.inspect
 => "#<Foo:0x0000010185f7d0 @bar=2, @baz=9>" 


Is that reasonable or is there a more idiomatic way of accomplishing this task?

cr