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Contents
##
# File: <gem-root>/lib/skn_utils/configurable.rb
# Ref: https://www.toptal.com/ruby/ruby-dsl-metaprogramming-guide
#
module SknUtils
# In the end, we have got ourselves a pretty neat module for making an arbitrary
# class configurable and then specifying those configuration values using a clean
# and simple DSL that also lets us reference one configuration attribute
# from another:
#
#################
# Inside Target component
#################
# class MyApp
# include SknUtils::Configurable.with(:app_id, :title, :cookie_name)
# # ...
# end
#
#################
# Inside Initializer
#################
# MyApp.configure do
# app_id "my_app"
# title "My App"
# cookie_name { "#{app_id}_session" }
# end
#
#################
# Usage:
#################
# MyApp.config.app_id # ==> "my_app"
#
# Here is the final version of the module that implements our DSL—a total of 36 lines of code:
module Configurable
def self.with(*attrs)
not_provided = Object.new
# Define the class/module methods
config_class = Class.new do
attrs.each do |attr|
define_method attr do |value = not_provided, &block|
if value === not_provided && block.nil?
result = instance_variable_get("@#{attr}")
result.is_a?(Proc) ? instance_eval(&result) : result
else
instance_variable_set("@#{attr}", block || value)
end
end
end
attr_writer *attrs
end
# Define the runtime access methods
class_methods = Module.new do
define_method :config do
@config ||= config_class.new
end
def configure(&block)
config.instance_eval(&block)
end
end
# Apply the custom configuration
Module.new do
singleton_class.send :define_method, :included do |host_class|
host_class.extend class_methods
end
end
end # method
end # end module
end # End module
Version data entries
12 entries across 12 versions & 1 rubygems