A ruby DCI implementation using SimpleDelegator. This was extracted from a Rails app I'm working on. It's a very simple and straightforward implementation.
I'm well aware that this is not "true" DCI but I believe it to be in the spirit of DCI while avoiding the awfulness that is object.extend.
Using object.extend in Ruby has two severe problems, one that makes it not true DCI and another that makes it really really slow:
- There is no unextend
- It blows rubys method cache when used
A further comment on 2 is that it means EVERY time you call extend it blows Rubys ENTIRE method cache - it doesn't mean just the object you're extending, it means everything.
Add this line to your application's Gemfile:
And then execute:
Or install it yourself as:
$ gem install role_playing
Using it is as simple as defining (usually) a context like so:
class MoneyTransferring include RolePlaying::Context def initialize(from_account, to_account) @from_account = from_account @to_account = to_account end def call(amount) ## this is a little contrived I know ## it could be easily implemented using ## increment/decrement methods - just ## showing the block syntax here SourceAccount(@from_account) do |source_account| DestinationAccount(@to_account).deposit(source_account.withdraw(amount)) end end role :SourceAccount do def withdraw(amount) self.amount=self.amount-amount amount end end role :DestinationAccount do def deposit(amount) self.amount=self.amount+amount end end end
Basically a role is a class inheriting from RolePlayer::Role, roles can also be defined by themselves(outside a context) like this:
class MyRole < RolePlayer::Role def my_additional_method end end class MyOtherRole < RolePlayer::Role def my_other_method end end
And, if defined by themselves, they can be applied in a few ways:
## our data object which will play different roles (eg. get new/different behavior within a context) class MyDataObject end MyRole.played_by(MyDataObject) do |role| role.my_additional_method end
role = MyRole.played_by(MyDataObject) role.my_additional_method
several roles can be applied too like so:
[MyRole, MyOtherRole].played_by(MyDataObject) do |role| role.my_additional_method role.my_other_method end
role = [MyRole, MyOtherRole].played_by(MyDataObject) role.my_additional_method role.my_other_method
Within a context a role is defined by the role class method. The syntax sugar of applying a role - eg. MyRole(MyDataObject) do |role| - is only available within classes including the RolePlayer::Context module. This was the way I envisioned it - to basically keep all code concerning a context within the same file (and inside the context class).
Please read the specs for a better understanding. Also please look up DCI (data, context, interaction) for a better understanding of what this is trying to accomplish.
Theres an RSpec extension included which basically aliases RSpecs context to role so the language used in RSpec can be closer to DCI when testing these things. To use that extension just do require 'role_playing/rspec_role' in your spec_helper. Look at the specs in this gem to see what I mean.
Theres a Railtie that adds autoloading of directory "contexts", the idea is to put all contexts and roles in there (roles are defined within the surrounding context in the same file).
The structure would look like:
app/ assets/ -> contexts/ controllers/ helpers/ models/ ...
http://tonyarcieri.com/dci-in-ruby-is-completely-broken - on why extend is bad
http://vimeo.com/8235394 - the inventor himself talks about DCI
- Fork it
- Create your feature branch (
git checkout -b my-new-feature)
- Commit your changes (
git commit -am 'Add some feature')
- Push to the branch (
git push origin my-new-feature)
- Create new Pull Request