[ANN] fattr-2.0.0 (supporting class inheritable attributes)

NAME
  fattr.rb

INSTALL
  gem install fattrs

URIS
  http://github.com/ahoward/fattr
  http://rubyforge.org/projects/codeforpeople/
  http://codeforpeople.com/

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

  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 my 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

    - class inheritable attributes

  all this in 156 lines of code

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 name=>default pairs can be given
    #
      require 'fattr'

      class C
        fattrs 'x' => 0b101000, 'y' => 0b10
      end

      c = C.new
      z = c.x + c.y
      p z #=> 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:0x2cd1c @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 << Logging
          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 << C
          fattr 'a' => 4
        end

        Fattr 'b' => 2
      end

      p [ C.a, C.b ].join

  ~ > ruby samples/g.rb

    "42"


  <========< samples/h.rb >========>

  ~ > cat samples/h.rb

    #
    # class variable inheritance is supported simply
    #
      require 'fattr'

      class A
        Fattr :x, :default => 42, :inheritable => true
      end

      class B < A
      end

      class C < B
      end

      p C.x #=> 42

      A.x = 42.0
      B.x = 'forty-two'

      p A.x #=> 42.0
      p B.x #=> 'forty-two'
      p C.x #=> 42

      C.x! # re-initialize from closest ancestor (B)

      p A.x #=> 42.0
      p B.x #=> 'forty-two'
      p C.x #=> 'forty-two'

  ~ > ruby samples/h.rb

    42
    42.0
    "forty-two"
    42
    42.0
    "forty-two"
    "forty-two"



HISTORY
  2.0.0:
    support class/module inheritable attributes

  1.1.0:
    ruby19 testing.  move to github.

  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


enjoy.