lib/hamster/immutable.rb
module Hamster
# @private
module Immutable
def self.included(klass)
klass.extend(ClassMethods)
klass.instance_eval do
include InstanceMethods
end
end
# @private
module ClassMethods
def new(*args)
super.__send__(:immutable!)
end
def memoize(*names)
include MemoizeMethods unless include?(MemoizeMethods)
names.each do |name|
original_method = "__hamster_immutable_#{name}__"
alias_method original_method, name
class_eval <<-METHOD, __FILE__, __LINE__
def #{name}
if @__hamster_immutable_memory__.instance_variable_defined?(:@#{name})
@__hamster_immutable_memory__.instance_variable_get(:@#{name})
else
@__hamster_immutable_memory__.instance_variable_set(:@#{name}, #{original_method})
end
end
METHOD
end
end
end
# @private
module MemoizeMethods
def immutable!
@__hamster_immutable_memory__ = Object.new
freeze
end
end
# @private
module InstanceMethods
def immutable!
freeze
end
def immutable?
frozen?
end
alias_method :__hamster_immutable_dup__, :dup
private :__hamster_immutable_dup__
def dup
self
end
def clone
self
end
protected
def transform_unless(condition, &block)
condition ? self : transform(&block)
end
def transform(&block)
__hamster_immutable_dup__.tap { |copy| copy.instance_eval(&block) }.immutable!
end
end
end
end