# module Multiton

# Multiton¶ ↑

Multiton design pattern ensures only one object is allocated for a given state.

The 'multiton' pattern is similar to a singleton, but instead of only one instance, there are several similar instances. It is useful when you want to avoid constructing objects many times because of some huge expense (connecting to a database for example), require a set of similar but not identical objects, and cannot easily control how many times a contructor may be called.

    class SomeMultitonClass
      include Multiton
      attr :arg
      def initialize(arg)
        @arg = arg
      end
    end

    a = SomeMultitonClass.new(4)
    b = SomeMultitonClass.new(4)   # a and b are same object
    c = SomeMultitonClass.new(2)   # c is a different object

## How It Works¶ ↑

A pool of objects is searched for a previously cached object, if one is not found we construct one and cache it in the pool based on class and the args given to the contructor.

A limitation of this approach is that it is impossible to detect if different blocks were given to a contructor (if it takes a block). So it is the constructor arguments only which determine the uniqueness of an object. To workaround this, define the class method ::multiton_id.

    def SomeMultitonClass.multiton_id(*args, &block)
      # ...
    end

Which should return a hash key used to identify the object being constructed as (not) unique.

### Public Instance Methods

clone() click to toggle source

Disable build-in copying methods.

    # File lib/facets/multiton.rb, line 135
    def clone
      raise TypeError, "can't clone Multiton #{self}"
      ##self
    end

dup() click to toggle source

    # File lib/facets/multiton.rb, line 140
    def dup
      raise TypeError, "can't dup Multiton #{self}"
      ##self
    end

### Protected Instance Methods

_dump(depth=-1) click to toggle source

Default marshalling strategy.

    # File lib/facets/multiton.rb, line 149
    def _dump(depth=-1)
      Marshal.dump(@multiton_initializer)
    end