Container.cr

Simple and small DI Container.

Installation

Add the dependency to your shard.yml:

dependencies:
  radbas-container:
    github: radbas/container.cr
    version: ~> 1.0

Run shards install

Usage

Extend the abstract Radbas::Container class and register/autowire your services:

require "radbas-container"

class MyService
  def initialize(
    @dep : DependencyService,
  ); end
end

class MyContainer < Radbas::Container
  # autowire does let you register namespaces
  # from which classes get resolved automatically
  autowire(MyApp, CustomNamespace)

  # register_subclasses registers all concrete subclasses of a given abstract class
  register_subclasses(MyAbstractClass, public: false)

  # register a single service
  register(DependencyService)

  # a factory can be used for setup
  register(MyService, factory: -> {
    # you can call get inside a factory to resolve dependencies
    MyService.new(get(DependencyService))
  }, public: true)

  # or: params can be used to configure constructor params
  # register(MyService, params: {dep: get(DependencyService)})
end

By default, all registered services are private. Normally you would register a single class as a public entrypoint and call get on the container:

class MyContainer < Radbas::Container
  register(MyApplication, public: true)
end

container = MyContainer.new
app = container.get(MyApplication)
app.run
# ...

Behaviour

Services are created lazily on the first get and then reused: every container instance holds one instance per service. Resolving is fiber-safe.
Registrations belong to the container class they are made in. A container inheriting from another container can use and override the registrations of its parent.
Constructor arguments with a default value are left alone when their type is neither registered nor autowired. Nilable arguments (dep : Foo? = nil) receive Foo if it is registered.
Generic services can be registered (register(Repository(User))); type vars in their constructor resolve to the actual types.
Services with multiple initialize overloads, or with a typed splat argument (*deps : Foo), must be registered with a factory.
Structs can be registered, but get returns a copy of the cached value.
The container itself can be injected (@container : MyContainer), and get(Radbas::Container) returns the container itself.
Configuration errors (unresolvable types, missing registrations, abstract types without factory) are reported at compile time, as is calling get with a type that is not registered or not public.
At runtime, get raises a subclass of Radbas::Container::Error:
- Radbas::Container::CircularDependencyError when a service depends on itself (directly or indirectly)
- Radbas::Container::SubclassAccessError when called with an unregistered subclass of a registered service

Development

shards install
mkdir -p bin && crystal build -o bin/ameba lib/ameba/bin/ameba.cr
crystal spec
crystal tool format --check
bin/ameba

Contributing

Fork it (https://github.com/radbas/container.cr/fork)
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 a new Pull Request

Contributors

Johannes Rabausch - creator and maintainer

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