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@jmondo
Last active December 26, 2015 16:09
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simple delegator example from sfrails oct 2013
# it's all part of ruby!
require 'ostruct'
require 'delegate'
require 'forwardable'
require 'minitest/autorun' # can run rspec style tests with this, part of ruby
# ---------------------------------------------------------------------------------------------------------
# the classes
# using simple delegator with the country object /after/ this app has been made with bad dependency mgmt.
# we swap the country string 'FIN' out for a country object with Country.new('FIN')
# the parts of the app that expect a string still get a string and the parts that want a first-class object
# with its own methods and logic get what they want too.
class Account
extend Forwardable
attr_accessor :country, :name
def initialize(options)
@country = options[:country]
@name = options[:name]
end
def country
Country.new(@country) #=> 'FIN'
end
# works just like `delegate to:` in rails (with forwardable included)
def_delegators :country, :in_europe?, :in_united_states?, :country_name
end
class Country < SimpleDelegator
COUNTRIES = {
'FIN' => 'Finland'
}
def in_europe?
self == 'FIN'
end
def in_united_states?
self == 'USA'
end
def country_name
COUNTRIES[self]
end
end
class BillingInfo
attr_accessor :account
def initialize(options)
@account = options[:account]
end
# the super awesome OO app has tons of these
def gets_10_percent_off?
account.country == 'FIN'
end
end
# -----------------------------------------------------------------------
# the tests (just run ruby simple_delegator_example.rb and they will run)
describe Account do
let(:account) { Account.new(name: 'Fincorp inc, intl.', country: 'FIN') }
it "has a country code" do
assert_equal 'FIN', account.country
end
it "is in europe" do
assert account.in_europe?
end
it "is finland" do
assert_equal 'Finland', account.country_name
end
end
describe BillingInfo do
let(:account) { Account.new(name: 'Finnish co, inc, intl', country: 'FIN') }
let(:billing_info) { BillingInfo.new(account: account)}
it "gives 10% off for being in finland" do
assert billing_info.gets_10_percent_off?
end
it "gives full price for USA customer" do
account.country = 'USA'
refute billing_info.gets_10_percent_off?
end
end
# --------------------------------------------------------------------------------------------------------
# Can also be used to futureproof your code. Take basic objects like integers and wrap them in a Class.new
# so that down the line, you can add methods to the class. For now, they just act like their integer value.
class Money < SimpleDelegator
# add this method down the line
def in_dollars
self / 100.0
end
end
price = Money.new(100_00)
p price.in_dollars #=> 100.00
@sockmonk
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I really like the example of using this to improve a bad design and letting different parts of the app get a bare string or full object behavior. Makes it much easier and less risky to improve the code gradually.

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