=========
Immutable
=========

:Author: Garry Dolley
:Date: 09-21-2008
:Version: v0.2

The ``Immutable`` module provides a method (immutable_method) that let's one
declare method(s) as immutable.  That is, other code will not be able to
open your class and replace your method with one of the same name.

Child classes, however, can still override the method.  So this is not like
Java's "final" method modifier.

One can argue that in OOP, if you want to reimplement or extend a method, a
child class is the only place where you should be doing that anyway.

Alpha
-----

This code is very new and despite a pretty comprehensive spec, I'm sure there's
cases where someone can figure out how to defeat this.  So be it. :)

This code has been tested on the following systems:

* GNU/Linux (Ubuntu 8.04.1) with Ruby 1.8.6
* FreeBSD 7.0 with Ruby 1.8.6
* OpenBSD 4.3 with Ruby 1.8.6
* Mac OS X 10.5 with Ruby 1.8.6

Please see the Author section below and report any problems.

Motivation
----------

My motivation for writing something that provides what some may call "evil"
functionality of closed methods/classes came from my trials of trying to
improve Rails loading time by reimplementing some ActiveSupport methods in C
(Ruby extension).  I absolutely needed my C versions of certain methods to be
present, and not clobbered by ActiveSupport.  

So why didn't I just load my extension after ActiveSupport?  Because by then it
is too late.  Rails is already loaded, along with slow running methods that get
called over 10,000 times.  Run the profiler and see for yourself:

::

  ./script/performance/profiler "require 'config/environment'"

Releases
--------

The latest code is in git::

  * git://github.com/up_the_irons/immutable.git

Requirements
------------

* None

Optionals
---------

* RubyGems 1.2.0 or higher

Installation
------------

git
~~~

::

  git clone git://github.com/up_the_irons/immutable.git

Add the path where the repo was cloned on your filesystem to $RUBYLIB, or just
use the full path when you "require".  See "Getting Started" section.

RubyGems
~~~~~~~~

::

  gem sources -a http://gems.github.com
  sudo gem install up_the_irons-immutable


Getting Started
---------------

If you installed ``Immutable`` by cloning the git repo, put the path to the repo in
$RUBYLIB, then put::

  require 'lib/immutable'

at the top of your programs.  Alternatively, you can just require the full path
to immutable.rb and not mess with $RUBYLIB.

If you installed ``Immutable`` from RubyGems, put::

  require 'rubygems'
  require 'immutable'

at the top of your programs.

Using
-----

There's not much to say, so let me present a fully working example:

::

  require 'rubygems'
  require 'immutable'
  
  module Foo
    include Immutable
  
    def foo
      :foo
    end
  
    def bar
      :bar
    end
  
    immutable_method :foo, :bar
  end
  
Now methods foo() and bar() cannot be overridden by other code opening Foo and
reimplementing them.  So the following:

::

  module Foo
    def foo
      :baz
    end
  end

Will raise an error:

::

  Cannot override the immutable method: foo (Immutable::CannotOverrideMethod)

There is one option to immutable_method() called :silent.  If :silent is true,
no exception will be raised.  One can then do:

::

  module Foo
    include Immutable

    def foo
      :foo
    end

    immutable_method :foo, :silent => true
  end

  module Foo
    def foo
      :baz
    end
  end

  include Foo

  foo          # => :foo

foo() returns :foo, not :baz.  It did not allow itself to be overriden.  Using
:silent can bring a great deal of confusion to other developers wondering why
their method overrides aren't working.  I would consider using :silent bad
practice in all but very limited cases.  Use with extreme caution.

There is an alias for immutable_method() called immutable_methods() (plural).
Use whichever style you prefer.
  
To Do
-----

Make method_added immutable, as well as immutable_method.  Write tests to try
to "defeat" an immutable method, see if we can prevent it.

I finished my TODOs, cool.

Author
------

Garry C. Dolley

gdolley [at] NOSPAM- ucla.edu

AIM: garry97531

IRC: up_the_irons in #git and #caboose on Freenode (and usually many other
channels)

Formatting
----------

This README is formatted in reStructredText [RST]_.  It has the best
correlation between what a document looks like as plain text vs. its
formatted output (HTML, LaTeX, etc...).  What I like best is, markup doesn't
look like markup, even though it is.

.. [RST] http://docutils.sourceforge.net/rst.html

Copyright
---------

Copyright (c) 2008,2009 Garry C. Dolley

Immutable is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later 
version.

Immutable is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
details.

You should have received a copy of the GNU General Public License along with
Immutable; if not, write to the Free Software Foundation, Inc., 51 Franklin
Street, Fifth Floor, Boston, MA  02110-1301, USA