NAME

  attributes.rb

URIS

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

SYNOPSIS

  attributes.rb provides an attr_* like method will several user friendly
  additions.  attributes.rb is similar to the traits.rb package but sacrafices
  a few features for simplicity of implementation: attributes.rb is only 42
  lines of code.

  the implimentation of attributes.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.

SAMPLES

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

  ~ > cat samples/a.rb

    #
    # basic usage is like attr, but note that attribute defines three methods,
    # getter, setter, and query
    #
      require 'attributes'
    
      class C
        attribute 'a'
      end
    
      c = C.new
    
      c.a = 42              # setter
      p c.a                 # getter
      p 'forty-two' if c.a? # query
    
    #
    # also not that attribute(s) works as well for objects as classes
    #
      o = Object.new
      o.attribute 'answer' => 42
      p o.answer

  ~ > ruby samples/a.rb

    samples/a.rb:5:in `require': ./lib/attributes.rb:53: syntax error (SyntaxError)
      def attributes *a &b
                         ^
    ./lib/attributes.rb:64: syntax error	from samples/a.rb:5


  <========< 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.
    #
      require 'attributes'
    
      class C
        attribute :a => 42
        attribute(:b){ Float a }
      end
    
      c = C.new
    
      p c.a
      p c.b

  ~ > ruby samples/b.rb

    samples/b.rb:6:in `require': ./lib/attributes.rb:53: syntax error (SyntaxError)
      def attributes *a &b
                         ^
    ./lib/attributes.rb:64: syntax error	from samples/b.rb:6


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

  ~ > cat samples/c.rb

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

  ~ > ruby samples/c.rb

    samples/c.rb:4:in `require': ./lib/attributes.rb:53: syntax error (SyntaxError)
      def attributes *a &b
                         ^
    ./lib/attributes.rb:64: syntax error	from samples/c.rb:4


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

  ~ > cat samples/d.rb

    #
    # a nice feature is that all attributes 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
    # attribute traversal is very easy.
    #
      require 'attributes'
    
      class C
        attributes %w( x y z )
    
        def attributes
          self.class.attributes
        end
    
        def initialize
          attributes.each_with_index{|a,i| send a, i}
        end
    
        def to_hash
          attributes.inject({}){|h,a| h.update a => send(a)}
        end
    
        def inspect
          to_hash.inspect
        end
      end
    
      c = C.new
      p c.attributes 
      p c 
    
      c.x 'forty-two' 
      p c.x

  ~ > ruby samples/d.rb

    samples/d.rb:7:in `require': ./lib/attributes.rb:53: syntax error (SyntaxError)
      def attributes *a &b
                         ^
    ./lib/attributes.rb:64: syntax error	from samples/d.rb:7