module Multiton

The Multiton class extends Singleton Pattern to collection level The main purpose is to have a collection of sole instanses of a particular class Possible application: a cache mapped to some DB

Usage¶ ↑

To use Multiton, include it in your class

class Klass
  include Multiton
  # ...
end

A single instance identified by some <ID> is created upon the first call of Klass.create() This ensures that there’s only one instance of the Klass for a given <ID>

a, b = Klass.create(:id), Klass.create(:id)
a == b
# => true
a.id == b.id
# => true

Before the call to Klass.initialize, instance variable @id is assigned to <ID> obtained from Klass.create

class Klass
  include Multiton
  attr_reader :ID

  def initialize
    @ID = @id
  end
end

a = Klass.create(:id)
a.ID == a.id
# => true
a.ID == :id
# => true

Attributes

id[R]

Public Class Methods

__init__(klass) click to toggle source

# File lib/multiton.rb, line 56
def __init__(klass)
  klass.instance_eval {
    @multiton__instances__ = {}
    @multiton__mutex__ = Mutex.new
  }

  def klass.new(id, *args, &blk)
    o = allocate
    o.instance_variable_set(:@id, id)
    o.instance_eval{initialize(*args, &blk)}
    o
  end

  def klass.inherited(sub)
    super
    Multiton.__init__(sub)
  end

  def klass.create(id, *args, &blk)
    return @multiton__instances__[id] if @multiton__instances__[id]
    @multiton__mutex__.synchronize {
      return @multiton__instances__[id] if @multiton__instances__[id]
      @multiton__instances__[id] = new(id, *args, &blk)
    }
    @multiton__instances__[id]
  end

  def klass.destroy(id)
    @multiton__mutex__.synchronize {
      return @multiton__instances__.delete id
    }
  end

  def klass.has_key?(id)
    @multiton__instances__.has_key? id
  end

  def klass.each(*args, &block)
    __instances__ = nil
    @multiton__mutex__.synchronize {
      __instances__ = @multiton__instances__.clone
    }
    __instances__.each *args, &block
  end

  def klass.to_a
    instances = []
    each { |k, v| instances << v }
    instances
  end

  def klass.[](id)
    create id
  end

  klass
end

Private Class Methods

append_features(mod) click to toggle source

Calls superclass method

# File lib/multiton.rb, line 119
def append_features(mod)
  #  help out people counting on transitive mixins
  unless mod.instance_of?(Class)
    raise TypeError, "Inclusion of the Multiton module in module #{mod}"
  end
  super
end

included(klass) click to toggle source

Calls superclass method

# File lib/multiton.rb, line 127
def included(klass)
  super
  Multiton.__init__(klass)
  klass.private_class_method :new, :allocate, :inherited
end

Public Instance Methods

_dump(depth = -1) click to toggle source

# File lib/multiton.rb, line 51
def _dump(depth = -1)
  raise TypeError, "can't marshall instance of singleton #{self.class}"
end

clone() click to toggle source

# File lib/multiton.rb, line 43
def clone
  raise TypeError, "can't clone instance of singleton #{self.class}"
end

dup() click to toggle source

# File lib/multiton.rb, line 47
def dup
  raise TypeError, "can't dup instance of singleton #{self.class}"
end