Diana - Lazy Dependency Injection

This module offers a DSL designed for the lazy resolution of dependency injections.

It facilitates efficient and deferred initialization of dependencies, ensuring that resources are only allocated when necessary.

This approach optimizes performance of application.

• Lazy Initialization: Dependencies are lazily initialized, ensuring they are only loaded when you need them, optimizing performance
• Transparent Behavior: No hidden or undocumented behaviors, providing a clear and predictable experience
• Flexible Integration: No dependencies, no mandatory DI container, but you can seamlessly integrate with any container of your choice.
• Broad Compatibility: Supports a wide range of Ruby versions, including 2.6 to 3.3, head, JRuby-9.4, and TruffleRuby-24.

These features are designed to make your development process smoother and more efficient!

bundle add diana

The Diana gem provides a streamlined way to define and manage dependencies in your Ruby application.

Use the .dependencies method to define your dependencies. You can also use the .dependency alias if you prefer.

class SomeClass
  include Diana.dependencies(
    foo: proc { Foo.new },
    bar: proc { Bar.new }
  )

  def some_method
    foo # => Foo.new
    bar # => Bar.new
  end
end

Dependencies are lazily initialized, meaning they are only loaded when accessed for the first time.

By default, dependency methods are private. You can change this behavior by configuring the Diana module:

Diana.methods_visibility = :public # private, public, protected

Using public methods can be more convenient in tests, allowing you to access the real dependency and stub its methods, rather than overwriting the dependency entirely. This approach helps ensure you are testing the correct dependency.

Classes with included dependencies can be nested. Dependencies from parent and child classes are merged.

Diana.dependencies method can be used multiple times. In this case dependencies are merged.

class SomeClass
  include Diana.dependencies(foo: proc { Foo.new })
  include Diana.dependencies(bar: proc { Bar.new })
end

• Dependency Storage: The @_diana_dependencies class variable holds the provided dependencies.
• Initialization: An #initialize method is added to handle dependency injection.
• Reader Methods: Private (by default) reader methods for dependencies are created.
• Lazy Resolution: Dependencies are resolved upon first access using a configurable resolver.

Here is an example of dependency injection and the final pseudo-code generated by the gem:

class SomeClass
  include Diana.dependencies(
    foo: proc { Foo.new },
    bar: proc { Bar.new }
  )
end

# Generated pseudo-code:
class SomeClass
  @_diana_dependencies = {
    foo: proc { Foo.new },
    bar: proc { Bar.new }
  }

  # handles dependency injection
  def initialize(foo: nil, bar: nil)
    @foo = foo if foo
    @bar = bar if bar
  end

  # handles inheritance
  def self.inherited(subclass)
    subclass.include Diana.dependencies(@_diana_dependencies)
    super
  end

  private

  # handles lazy `foo` resolution
  def foo
    @foo ||= Diana.resolve(self.class.instance_variable_get(:@_diana_dependencies)[:foo])
  end

  # handles lazy `bar` resolution
  def bar
    @bar ||= Diana.resolve(self.class.instance_variable_get(:@_diana_dependencies)[:bar])
  end
end

This structure ensures efficient and flexible dependency management.

The default resolver handles only procs, functioning as follows:

DEFAULT_RESOLVER = proc do |dependency|
  dependency.is_a?(Proc) ? dependency.call : dependency
end

You can customize the resolver to fit your needs. For instance, to resolve strings to a DI container, you can modify the resolver like this:

Diana.resolver = proc do |dependency|
  case dependency
  when String then DI_CONTAINER[dependency]
  when Proc then dependency.call
  else dependency
  end
end

SomeClass.include Diana.dependencies(foo: 'utils.foo') # => DI_CONTAINER['utils.foo']

• This gem is intended for use with classes that have no manually defined #initialize method. This design choice prevents conflicts or unpredictable behavior with custom #initialize methods. If you do add a custom #initialize method, it will take precedence. In such cases, ensure you include a super(**deps) call to override dependencies if needed.

• We avoid calling super in the added #initialize method to prevent the need for arguments modifications, which could negatively impact performance.

These limitations ensure that the gem remains predictable and performant, avoiding any hidden complexities or unexpected behaviors.

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

The gem is available as open source under the terms of the MIT License.