Contents

---
title: How does it work?
layout: gem-single
name: dry-auto_inject
---

dry-auto\_inject enables _constructor dependency injection_ for your objects. It achieves this by defining two methods in the module that you include in your class.

First, it defines `.new`, which resolves your dependencies from the container, if you haven't otherwise provided them as explicit arguments. It then passes these dependencies as arguments onto `#initialize`, as per Ruby’s usual behaviour.

It also defines `#initialize`, which receives these dependencies as arguments and then assigns them to instance variables. These variables are made available via `attr_reader`s.

So when you specify dependencies like this:

```ruby
Import = Dry::AutoInject(MyContainer)

class MyClass
  include Import["users_repository"]
end
```

You’re building something like this (this isn’t a line-for-line copy of what is mixed into your class; it’s intended as a guide only):

```ruby
class MyClass
  attr_reader :users_repository

  def self.new(**args)
    deps = {
      users_repository: args[:users_repository] || MyContainer["users_repository"]
    }

    super(**deps)
  end

  def initialize(users_repository: nil)
    super()

    @users_repository = users_repository
  end
end
```

Since these methods are defined in the module that you include in your class, you can still override them in your class if you wish to provide custom behavior.

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
dry-auto_inject-0.7.0	docsite/source/how-does-it-work.html.md