overlay_tag.adoc

Overlaying tags (overlay_tag)

Instead of overlaying services directly, it’s often useful to overlay all services with a given tag.

require 'alki'

assembly = Alki.create_assembly do
  overlay_tag :exclaimed, :exclaim, 3

  tag :exclaimed
  service :greeting do
    'Hello World'
  end

  factory :exclaim do
    -> (string,count) do
      string + ('!' * count)
    end
  end
end

puts assembly.new.greeting

#output: Hello World!!!

Factories can access the tags of the services their being called from, allowing you to customize the build based on what tags are present

require 'alki'

assembly = Alki.create_assembly do
  overlay_tag :process, :process_string

  tag :process, exclaim: 3
  service :greeting do
    'Hello World'
  end

  factory :process_string do
    -> (string) do
      if exclaim = meta[:tags][:exclaim]
        string = string + ('!' * exclaim)
      end
      string
    end
  end
end

puts assembly.new.greeting

#output: Hello World!!!

Finally, tag overlays work even across assembly mounts, allowing overlays to be defined in a library, and then applied by tagging services.

require 'alki'

string_processor = Alki.create_assembly do
  overlay_tag :process, :process_string

  factory :process_string do
    -> (string) do
      if exclaim = meta[:tags][:exclaim]
        string = string + ('!' * exclaim)
      end
      string
    end
  end
end

assembly = Alki.create_assembly do
  mount :string_processor, string_processor

  tag :process, exclaim: 3
  service :greeting do
    'Hello World'
  end
end

puts assembly.new.greeting

#output: Hello World!!!