NAME attributes.rb

INSTALL gem install attributes

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

SYNOPSIS attributes.rb provides a set of attr_* like method with several user friendly additions. attributes.rb is similar to the traits.rb package but sacrifices a few features for simplicity of implementation.

the implementation 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 along with concepts from the original traits lib

key features provided by attributes 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 attributes they've defined and this information is
 available to client code

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

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

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

- attributes can be defined on objects on a per singleton basis as well

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

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

all this in < 100 lines of code

HISTORY 5.0.0

• added support for block caching. for example

  - simple block caching:
  
      class Filter 
        attribute :process
      end
  
      filter = Filter.new
  
      filter.process{|line| line.upcase}
  
      lines.each do |line|
        p filter.process.call(line)
      end
  
  - using block caching to delay block evaluation/class-factory:
  
      module MigrationDSL
        attribute :migration
  
        def migration_class
          model = self
  
          Class.new(::ActiveRecord::Migration) do
            singleton_class =
              class << self
                self
              end
            singleton_class.module_eval{ attribute :model => model }
            singleton_class.module_eval &model.migration
          end
        end
      end
  
      class Table < ActiveRecord::Base
        extend MigrationDSL
      end
  
      class Jobs < Table
        migration do
          def up
            create_table model.table_name, :primary_key => model.primary_key do |t|
              t.column 'vinyl_shoes', :text
            end
          end
  
          def down
            create_table model.table_name
          end
        end
      end
  
      ...
  
      JobsMigration = Jobs.migration_class

  4.1.0

• 4.0.0 introduced a bug where a query (foo?) would not initialize a var - 4.1.0 fixes that

  4.0.0

• removed dependancy on, and bundle of, pervasives
• faster. as fast as normal method definition.

• faster lookup for MyClass.attributes.include?('foobar')

  3.7.0 small patch to use 'instance_variable_defined?' instead of defined? keyword

  3.5.0 migrated to a pervasives based impl to attributes should work on any object - even blankslate objects

  3.3.0

  moved to an instance variable-less model using an module level closure for the attributes list

SAMPLES @samples