Outputs

Outputs are the results of a service.

TL;DR

• Define outputs using the output keyword in the service class

• Outputs can have default values

• Outputs can be validated by type (validated when the service succeeds)

Define Outputs

You define outputs using the output keyword in the service class.

class AI::Chat < ApplicationService
  output :messages
  output :cost
end

Write Outputs

Outputs function similarly to instance variables created with attr_accessor.

class AI::Chat < ApplicationService
  # Steps
  step :chat

  # Outputs
  output :messages
  output :cost

  private

  def chat
    self.messages = ["Hello!", "Hi, how are you?"]
    self.cost = 0.0013
  end
end

To set outputs programmatically, use the outputs.set method or hash syntax.

class AI::Chat < ApplicationService
  # ...

  def chat
    outputs.set(:messages, ["Hello!", "Hi, how are you?"])
    outputs.set(:cost, 0.0013)

    # Or use hash syntax

    outputs[:messages] = ["Hello!", "Hi, how are you?"]
    outputs[:cost] = 0.0013
  end
end

Type Validation

You can specify the type of output using the type option. The output type will be validated when the service successfully completes.

class AI::Chat < ApplicationService
  output :messages, type: Array
  output :cost, type: Float
end

You can specify multiple allowed types using an array.

class AI::Chat < ApplicationService
  output :result, type: [String, Hash]
end

Type Enforcement (Enabled by Default)

By default, all outputs must have a type option. This helps catch type-related bugs early and makes your services self-documenting.

class MyService < ApplicationService
  output :result, type: Hash  # ✓ Valid
  output :data                # ✗ Raises MissingTypeError
end

To disable type enforcement for outputs in a specific service:

class LegacyService < ApplicationService
  config require_output_type: false
  
  output :data             # Allowed when require_output_type is disabled
end

See the Configuration documentation for more details.

Sorbet Runtime Types

Outputs support Sorbet runtime types for type validation:

require "sorbet-runtime"

class AI::Chat < ApplicationService
  output :messages, type: T::Array[Hash]
  output :total_tokens, type: T::Utils.coerce(Integer)
  output :metadata, type: T.nilable(Hash), optional: true
end

See the Sorbet Runtime Types documentation for more details.

Default Values

Set default values for outputs using the default option. The default value will be automatically set before the execution of steps.

class AI::Chat < ApplicationService
  output :cost, default: 0.0
end

Removing Inherited Outputs

When inheriting from a parent service, you can remove outputs using remove_output:

class BaseReportService < ApplicationService
  output :report
  output :debug_info
end

class ProductionReportService < BaseReportService
  # Don't expose debug info in production
  remove_output :debug_info
end

What's Next?

Next, learn about context.

Next: Context