Shirinji

Dependencies Injection made clean and easy for Ruby.

Supported ruby versions

• 2.7.x
• 3.0.x

Principles

Remove hard dependencies between your objects and delegate object tree building to an unobtrusive framework with cool convention over configuration.

Shirinji relies on a mapping of beans and a resolver. When you resolve a bean, it will return (by default) an instance of the class associated to the bean, with all the bean dependencies resolved.

class FooService
  attr_reader :bar_service
  
  def initialize(bar_service:)
    @bar_service = bar_service
  end
  
  def call(obj)
    obj.foo = 123
    
    bar_service.call(obj)
  end
end

map = Shirinji::Map.new do
  bean(:foo_service, klass: 'FooService')
  bean(:bar_service, klass: 'BarService')
end

resolver = Shirinji::Resolver.new(map)

resolver.resolve(:foo_service)
# => <#FooService @bar_service=<#BarService>> 

Shirinji is unobtrusive. Basically, any of your objects can be used outside of its context.

bar_service = BarService.new
foo_service = FooService.new(bar_service: bar_service)
# => <#FooService @bar_service=<#BarService>>

# tests

RSpec.describe FooService do
  let(:bar_service) { double(call: nil) }
  let(:service) { described_class.new(bar_service: bar_service) }
  
  describe '.call' do
    # ...
  end
end

Constructor arguments

Shirinji relies on constructor to inject dependencies. It's considering that objects that receive dependencies should be immutables and those dependencies should not change during your program lifecycle.

Shirinji doesn't accept anything else than named parameters. This way, arguments order doesn't matter and it makes everybody's life easier.

Name resolution

By default, when you try to resolve a bean, Shirinji will look for a bean named accordingly for each constructor parameter.

It's possible to locally override this behaviour though by using attr macro.

class FooService
  attr_reader :bar_service
  
  def initialize(my_service:)
    @bar_service = my_service
  end
end

map = Shirinji::Map.new do
  bean(:foo_service, klass: 'FooService') do
    attr :my_service, ref: :bar_service
  end
  
  bean(:bar_service, klass: 'BarService')
end

resolver = Shirinji::Resolver.new(map)

resolver.resolve(:foo_service)
# => <#FooService @bar_service=<#BarService>>

Caching and singletons

Shirinji provides a caching mecanism to help you improve memory consumption. This cache is safe as long as your beans remains immutable (they should always be).

The consequence is that any cached instance is actually a singleton. Singleton is no more a property of your class but of it's environment, improving the reusability of your code.

Singleton is the default access mode for a bean.

map = Shirinji::Map.new do
  bean(:bar_service, klass: 'BarService', access: :instance)
  bean(:foo_service, klass: 'FooService', access: :singleton)
  # same as bean(:foo_service, klass: 'FooService')
end

resolver = Shirinji::Resolver.new(map)

resolver.resolve(:foo_service).object_id #=> 1
resolver.resolve(:foo_service).object_id #=> 1

resolver.resolve(:bar_service).object_id #=> 2 
resolver.resolve(:bar_service).object_id #=> 3 

Cache can be reset with the simple command resolver.reset_cache, which can be useful when using a development console like rails console (shirinji-rails is attaching cache reset to reload! command).

Other type of beans

Dependencies injection doesn't apply only to classes. You can actually inject anything and therefore, Shirinji allows you to declare anything as a dependency. To achieve that, use the key value instead of class.

module MyApp
  def self.config
    @config
  end
  
  def self.load!
    @config = OpenStruct.new  
  end
end

class FooService
  attr_reader :config
  
  def initialize(config:)
    @config = config
  end
end

MyApp.load!

map = Shirinji::Map.new do
  bean(:config, value: Proc.new { MyApp.config })
  
  bean(:foo_service, klass: 'FooService')
end

resolver = Shirinji::Resolver.new(map)

resolver.resolve(:foo_service)
#=> <#FooService @config=<#OpenStruct ...> ...>

A value can be anything. Proc will be lazily evaluated. It also obeys the cache mechanism described before.

Skip construction mechanism

In some cases, you need a dependency to be injected as a class and not an instance. In such case, you could use value beans, returning the class itself, but you would lose the benefit of scopes (see below). Instead, Shirinji provides a parameter to skip the object construction.

A real life example is a Job where deliver_now and deliver_later are class methods.

map = Shirinji::Map.new do
  bean(:foo_job, klass: 'FooJob', construct: false)
end

resolver = Shirinji::Resolver.new(map)

resolver.resolve(:foo_job) #=> FooJob

Scopes

Building complex objects mapping leads to lot of repetition. That's why Shirinji also provides a scope mechanism to help you dry your code.

map = Shirinji::Map.new do
  scope module: :Services, suffix: :service, klass_suffix: :Service do
    bean(:foo, klass: 'Foo')
    # same as bean(:foo_service, klass: 'Services::FooService')
    
    scope module: :User, prefix: :user do
      bean(:bar, klass: 'Bar')
      # same as bean(:user_bar_service, klass: 'Services::User::BarService')
    end 
  end
end

Scopes also come with an auto_klass attribute to save even more time for common cases

map = Shirinji::Map.new do
  scope module: :Services, 
        suffix: :service, 
        klass_suffix: :Service, 
        auto_klass: true do
    bean(:foo)
    # same as bean(:foo_service, klass: 'Services::FooService')
  end
end

Scopes also provides an auto_prefix option

map = Shirinji::Map.new do
  scope module: :Services, 
        suffix: :service, 
        klass_suffix: :Service, 
        auto_klass: true do
        
    # Do not use auto prefix on root scope or every bean will be prefixed
    # with `services_`
    scope auto_prefix: true do
      bean(:foo)
      # same as bean(:foo_service, klass: 'Services::FooService')
      
      scope module: :User do
        # same as scope module: :User, prefix: :user
  
        bean(:bar)
        # same as bean(:user_bar_service, klass: 'Services::User::BarService')
      end
    end
  end
end

Finally, for mailers / jobs ..., Scopes allow you to specify a global value for construct

map = Shirinji::Map.new do
  scope module: :Jobs, 
        suffix: :job, 
        klass_suffix: :Job, 
        auto_klass: true, 
        construct: false do
    bean(:foo)
    # bean(:foo_job, klass: 'Jobs::FooJob', construct: false)
  end
end

Scopes do not carry property access

Code splitting

When a project grows, dependencies grows too. Keeping them into one single file leads to headaches. One possible solution to keep everything under control is to split your dependencies into many files.

To include a "sub-map" into another one, you can use include_map method.

# dependencies/services.rb
Shirinji::Map.new do
  bean(:foo_service, klass: 'FooService')
end

# dependencies/queries.rb
Shirinji::Map.new do
  bean(:foo_query, klass: 'FooQuery')
end

# dependencies.rb

root = Pathname.new(File.expand_path('../dependencies', __FILE__))

Shirinji::Map.new do
  bean(:config, value: -> { MyApp.config })
  
  # paths must be absolute 
  include_map(root.join('queries.rb'))
  include_map(root.join('services.rb'))
end

Notes

• It is absolutely mandatory for your beans to be stateless to use the singleton mode. If they're not, you will probably run into trouble as your objects behavior will depend on their history, leading to unpredictable effects.
• Shirinji only works with named arguments. It will raise ArgumentError if you try to use it with "standard" method arguments.

TODOS

• solve absolute paths problems for include_map (instance_eval is a problem)

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/fdutey/shirinji.