Basic usage

Requirements

You need only one thing before you can use dry-auto_inject: a container to hold your application’s dependencies. These are commonly known as “inversion of control” containers.

A dry-container will work well, but the only requirement is that the container responds to the #[] interface. For example, my_container["users_repository"] should return the “users_repository” object registered with the container.

Creating an injector

To create an injector, pass the container to Dry::AutoInject:

Import = Dry::AutoInject(my_container)

Assign the injector to a constant (or make it globally accessible somehow) so you can refer to it from within your classes.

Specifying dependencies

To specify the dependencies for a class, mix in the injector and provide the container identifiers for each dependency:

class MyClass
  include Import["users_repository", "deliver_welcome_email"]
end

Using dependencies

Each dependency is available via a reader with a matching name:

class MyClass
  include Import["users_repository"]

  def call
    puts users_repository.inspect
  end
end

If your container identifiers include delimiters (like ".") or other characters that are not allowed within variable or method names, then the final part of the name will be used instead:

class MyClass
  include Import["repositories.users"]

  def call
    puts users.inspect
  end
end

Specifying aliases for dependencies

You can specify dependencies as a hash to provide your own names for each one:

class MyClass
  include Import[users_repo: "repositories.users"]

  def call
    puts users_repo.inspect
  end
end

If you want to provide a mix of inferred names and aliases, provide the aliases last:

class MyClass
  include Import[
    "repositories.users",
    deliver_email: "operations.deliver_welcome_email",
  ]
end

Initializing your object

Initialize your object without any arguments and all the dependencies will be resolved from the the container automatically:

my_obj = MyClass.new

Passing manual dependencies

To provide an alternative object for a dependency, pass it to the initializer with a keyword argument matching the dependency’s name:

class MyClass
  include Import["repositories.users"]
end

my_obj = MyClass.new(users: different_repo)

This technique is useful when testing your class in isolation. You can pass in test doubles to verify your class’ behaviour under various different circumstances.