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ServiceProvider

Simple attempt to inject dependencies through method decorators (https://github.com/michaelfairley/method_decorators) or meta programming.

Installation

Add this line to your application's Gemfile:

gem 'service_provider'

And then execute:

$ bundle

Or install it yourself as:

$ gem install service_provider

Usage

Service provider comes with an automatic service provider, which registers every provided service under its name. You can specify your own service provider (see below).

Providing a service

The class that provides a dependency has to extend the ServiceProvider module and to decorate its initialize method with the Provides decorator:

class SquareService
  extend ServiceProvider

  +Provides
  def initialize
  end
end

The (suggested) name of the service provided defaults to the underscored class name, and can also be given as a parameter: +Provides.new(:square_service). The standard service provider used will use this name as the name of the service. Custom service providers (see below) might not make use of this information.

Using a service

The class that requires a service has to extend the MethodDecorators module and to decorate its initialize method with the Requires decorator. The argument passed into the Requires decorator will be the name of the getter that will return that service.

class SquareSample
  extend MethodDecorators

  +Requires.new(:square_service)
  def initialize
  end

  def do_work(num)
    square_service.square(num)
  end
end

You can also use the require_service method to inject a service. You will have to use this method if your instances are not created with a call to Class.new, but with a call to Class.allocate. This is the case for all instances of ActiveRecord::Base that are returned from a find call. See here for some information about that

class SquareSample

  require_service(:square_service)
  
  def do_work(num)
    square_service.square(num)
  end
end

After a service has been required it can be manually set on the object, through a setter for the instance variable, i.e. square_service=.

Using a custom service provider

You might want to specify how services are provided when you have multiple classes that implement the same service or when you want to change the implementations completely, i.e. for tests. To do so, provide your own service provider and register it with ServiceProvider:

class CustomServiceProvider
  def provide(service_class, service_class_provided_service_name)
    #how to store services
  end

  def get_service(service_name)
    #how to retrieve services by name
  end
end

ServiceProvider.provider_implementation = CustomServiceProvider.new

Known limitatations and uglinesses

  • Each class has to have an empty constructor to put the MethodDecorators before it.
  • Provider has to extend the ServiceProvider, Requirer has to extend MethodDecorators

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

License

Copyright (c) Johannes Tuchscherer

Released under the MIT license. See LICENSE file for details.