DeclarativeInitialization

Boilerplate slows down devs and irritates everyone, plus the added cruft makes it harder to scan for the actual logic in a given file.

This is a small layer to support declarative initialization specifically for simple keyword-based classes.

Given a standard ruby class like so:

class SomeObject
  def initialize(foo:, bar:, baz: "default value")
    @foo = foo
    @bar = bar
    @baz = baz
  end

  attr_reader :foo, :bar, :baz
end

With this library it can be simplified to:

class SomeObject
  include DeclarativeInitialization

  initialize_with :foo, :bar, baz: "default value"
end

The gem name is declarative_initialization because there's already a very outdated gem claiming the initialize_with name.

We've set up an alias, however, so you can do either include DeclarativeInitialization or include InitializeWith.

FWIW in practice at Teamshares we just include DeclarativeInitialization in the base class for all our View Components.

Sometimes the existing initialize method also does other work, for instance setting initial values for additional instance variables that aren't passed in directly.

We support that by passing an optional block to initialize_with -- for instance, in the example above if the original version also set @bang = foo * bar, we could support that by changing the updated version to:

initialize_with :foo, :bar, baz: "default value" do
  @bang = @foo * @bar
end

• Accepting a block: this is handled automatically -- if a block was provided to the Foo.new call, it'll be made available as @block/attr_reader :block

• If a method with same name already exists, we log a warning and do not create the attr_reader. In that case you'll need to reference the instance variable directly.

  • Because of this, best practice when referencing variables in the post-initialize block is to use @foo rather than relying on the foo attr_reader

• Due to ruby syntax limitations, we do not support referencing other fields directly in the declaration:

  • Does not work:

    initialize_with :user, company: user.employer

  • Workaround:

    initialize_with :user, company: nil do
      @company ||= @user.employer
    end

• If using initialize_with on a subclass where the superclass defines initialize, we will not automatically call super, because if we do we get this RuntimeError:

  implicit argument passing of super from method defined by define_method() is not supported. Specify all arguments explicitly.

• If you need to call super from the block passed into initialize_with (unusual edge case, subclass requires different arguments than parent):

  • Does not work (due to instance_exec changing execution context but not the method lookup chain):

    initialize_with :foo do
      super(bar: 123)
    end

  • Workaround possible (but really, probably more understandable to just fall back to manually writing def initialize):

    initialize_with :foo do
      parent_initialize = method(:initialize).super_method
      parent_initialize.call(bar: 123)
    end

• If you find yourself backed into a weird corner, just use a plain ole def initialize! This library is meant to make the easy cases less work, but there's no requirement that you must use it for every super complex case you run into. :)

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/teamshares/declarative_initialization. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

Everyone interacting in the DeclarativeInitialization project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.