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Contents
require 'caruby/util/collection'
require 'caruby/util/validation'
# A DomainExtent contains class-specific key => object associations.
# The objects are created on demand and accessed by the get method.
#
# @example
# DomainExtent.new { |klass, key| key.to_s + klass.name }.get(String, 'a') #=> aString
class DomainExtent < LazyHash
# Creates a new DomainExtent. The block passed to the constructor
# is a factory to create an object on demand, with arguments
# the target class and the target key. The default block is empty.
def initialize
return initialize {} unless block_given?
super { |klass| LazyHash.new { |key| yield klass, key } }
end
# Sets the factory used to create an instance of the specified class.
# The factory is called to create a new instance when a get operation
# does not yet have a key => instance association.
#
# The factory accepts a single argument, the instance key, e.g.
# set_factory(MyClass) { |key| MyClass.new(key) }
def set_factory(klass, &factory)
# the current instances, if any
instances = fetch(klass) if has_key?(klass)
# make the key => instance class extent map
# the instance creation factory is
class_extent = LazyHash.new { |key| yield key }
# copy existing instances if necessary
class_extent.merge!(instances) if instances
# add the class => class extent association
self[klass] = class_extent
end
# Returns the domain instance of the given class for the given key.
# If there is nois no entry for key and the factory is set for the class,
# then a new object is created on demand.
def get(klass, key)
raise RuntimeError.new("Invalid target class: #{klass}") unless klass.is_a?(Class)
raise RuntimeError.new("Missing target key value") if key.nil?
# the class extent hash is created on demand if necessary.
# the instance is created on demand if there is a factory for the class.
self[klass][key]
end
end
Version data entries
6 entries across 6 versions & 1 rubygems