Shoot footing fun, ported from JavaScript

gistfile1.rbx

require 'rubygems'
require 'metaid' # always a good idea
require 'spec'

Object.class_eval do
  def with(hash)
    hash.each do |key, value|
      meta_def(key) { hash[key] }
      meta_def("#{key}=") { |v| hash[key] = v }
    end
    
    return unless block_given?
    
    result = yield
    
    hash.each do |key, value|
      meta_eval { remove_method(key) }
      meta_eval { remove_method("#{key}=") }
    end
    
    result
  end
end

describe "with" do
  def ok; :out end
  
  before(:each) do
    @hash = { :foo => :bar, :ok => :in }
  end
  
  it "should just define methods when no block given" do
    with({ :fizz => :buzz })
    fizz.should == :buzz
  end
  
  it "should make hash keys available in context" do
    with(@hash) { foo }.should == :bar
  end
  
  it "should remove methods outside with context" do
    with(@hash) { foo }
    proc { foo }.should raise_error
  end
  
  it "should preserve other defined methods" do
    ok.should == :out
    with(@hash) { ok }.should == :in
    ok.should == :out
  end
  
  it "should allow setters" do
    @hash[:foo].should == :bar
    with(@hash) { self.foo = :set }
    @hash[:foo].should == :set
  end
  
  it "should remove setters" do
    with(@hash) { foo }
    proc { self.foo = :set }.should raise_error
  end
end