NAME
  fattr.rb

INSTALL
  gem install fattrs

URIS
  http://codeforpeople.com/lib/ruby
  http://rubyforge.org/projects/codeforpeople/
  http://codeforpeople.rubyforge.org/svn/

SYNOPSIS
  fattr.rb is a "fatter attr" for ruby.

  fattr.rb supercedes attributes.rb as that library, even though it added only
  one method to the global namespace, collided too frequently with user code -
  in particular rails' code.

  the implementation of fattr.rb borrows many of the best ideas from the
  metakoans.rb ruby quiz

    http://www.rubyquiz.com/quiz67.html

  in particular the solutions of Christian Neukirchen and Florian Gross along
  with concepts from the original traits.rb lib

  key features provided by fattrs are

    - ability to specify default values for attrs and definition time.  values
      can be literal objects or blocks, which are evaluated in the context of
      self to initialize the variable

    - classes remember which fattrs they've defined and this information is
     available to client code

    - a whole suite of methods is defined by calls to #fattrs including
     getter, setter, query (var?) and banger (var! - which forces
     re-initialization from the default value/block)

    - ability to define multiple fattrs at once using key => value pairs

    - fast lookup of whether or not a class has defined a certain fattr

    - fattrs can be defined on objects on a per singleton basis

    - getters acts as setters if an argument is given to them

    - block caching, calling an fattr with a block sets the instance
      variable to that block

    - shortcuts for adding class/module level fattrs

  all this in < 100 lines of code

HISTORY
  1.0.2:
    added Fattr shortcut for adding class/module level fattrs

      class C
        Fattr 'children' => []

        def C.inherited other
          (children << other).uniq!
          super
        end
      end

      class B < C
      end

      p C.children #=> B

  1.0.0:
    port from attributes.rb retaining all the same features of that version of
    attributes.rb

SAMPLES

  <========< samples/a.rb >========>

  ~ > cat samples/a.rb

    #
    # basic usage is like attr, but note that fattr defines a suite of methods
    #
      require 'fattr'
    
      class C
        fattr 'a'
      end
    
      c = C.new
    
      c.a = 42
      p c.a                 #=> 42
      p 'forty-two' if c.a? #=> 'forty-two'
    
    #
    # fattrs works on object too 
    #
      o = Object.new
      o.fattr 'answer' => 42
      p o.answer           #=> 42

  ~ > ruby samples/a.rb

    42
    "forty-two"
    42


  <========< samples/b.rb >========>

  ~ > cat samples/b.rb

    #
    # default values may be given either directly or as a block which will be
    # evaluated in the context of self.  in both cases (value or block) the
    # default is set only once and only if needed - it's a lazy evaluation.  the
    # 'banger' method can be used to re-initialize a variable at any point whether
    # or not it's already been initialized.
    #
      require 'fattr'
    
      class C
        fattr :a => 42
        fattr(:b){ Float a }
      end
    
      c = C.new
      p c.a #=> 42
      p c.b #=> 42.0
    
      c.a = 43
      p c.a #=> 43
      c.a!
      p c.a #=> 42

  ~ > ruby samples/b.rb

    42
    42.0
    43
    42


  <========< samples/c.rb >========>

  ~ > cat samples/c.rb

    #
    # multiple values may by given, plain names and key/val pairs may be mixed.
    #
      require 'fattr'
    
      class C
        fattrs 'x', 'y' => 0b101000, 'z' => 0b10
      end
    
      c = C.new
      c.x = c.y + c.z
      p c.x #=> 42

  ~ > ruby samples/c.rb

    42


  <========< samples/d.rb >========>

  ~ > cat samples/d.rb

    #
    # a nice feature is that all fattrs are enumerated in the class.  this,
    # combined with the fact that the getter method is defined so as to delegate
    # to the setter when an argument is given, means bulk initialization and/or
    # fattr traversal is very easy.
    #
      require 'fattr'
    
      class C
        fattrs %w( x y z )
    
        def fattrs
          self.class.fattrs
        end
    
        def initialize
          fattrs.each_with_index{|a,i| send a, i}
        end
    
        def to_hash
          fattrs.inject({}){|h,a| h.update a => send(a)}
        end
    
        def inspect
          to_hash.inspect
        end
      end
    
      c = C.new
      p c.fattrs 
      p c 
    
      c.x 'forty-two' 
      p c.x

  ~ > ruby samples/d.rb

    ["x", "y", "z"]
    {"x"=>0, "y"=>1, "z"=>2}
    "forty-two"


  <========< samples/e.rb >========>

  ~ > cat samples/e.rb

    #
    # my favourite element of fattrs is that getters can also be setters.
    # this allows incredibly clean looking code like
    #
      require 'fattr'
    
      class Config
        fattrs %w( host port)
        def initialize(&block) instance_eval &block end
      end
    
      conf = Config.new{
        host 'codeforpeople.org'
    
        port 80
      }
    
      p conf

  ~ > ruby samples/e.rb

    #<Config:0x224d4 @port=80, @host="codeforpeople.org">


  <========< samples/f.rb >========>

  ~ > cat samples/f.rb

    #
    # of course fattrs works as well at class/module level as at instance
    # level
    #
      require 'fattr'
    
      module Logging 
        Level_names = {
          0 => 'INFO',
          # ...
          42 => 'DEBUG',
        }
    
        class << self
          fattr 'level' => 42
          fattr('level_name'){ Level_names[level] }
        end
      end
    
    p Logging.level
    p Logging.level_name

  ~ > ruby samples/f.rb

    42
    "DEBUG"


  <========< samples/g.rb >========>

  ~ > cat samples/g.rb

    #
    # you can add class/module fattrs the 'normal' way or using the provided
    # shortcut method
    #
      require 'fattr'
    
      class C
        class << self
          fattr 'a' => 4
        end
    
        Fattr 'b' => 2
      end
    
      p [ C.a, C.b ].join

  ~ > ruby samples/g.rb

    "42"