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##
# Allows attributes to be declared as lazy, meaning that they won't be
# computed until they are asked for.
#
# Works by delegating each lazy_reader to a cached lazy_source method.
#
# class Person
# lazy_reader :eyes
#
# def lazy_source
# OpenStruct.new(:eyes => 2)
# end
# end
#
# >> Person.new.eyes
# => 2
#
module Lazy
def self.extended(klass)
klass.send(:attr_writer, :lazy_source)
end
def lazy_reader(*args)
args.each do |arg|
ivar = "@#{arg}"
define_method(arg) do
if instance_variable_defined?(ivar)
val = instance_variable_get(ivar)
return val if val
end
instance_variable_set(ivar, (@lazy_source ||= lazy_source).send(arg))
end
end
end
end
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