Current Time Algebraic Effect

time.rb

require 'dry/effects'

class CurrentTimeMiddleware
  include Dry::Effects::Handler.CurrentTime

  def initialize(app)
    @app = app
  end

  def call(env)
    # It will use Time.now internally once and set it fixed
    with_current_time do
      @app.(env)
    end
  end
end

###

class CreateSubscription
  include Dry::Efefcts.Resolve(:subscription_repo)
  include Dry::Effects.CurrentTime

  def call(values)
    subscription_repo.create(
      values.merge(start_at: current_time)
    )
  end
end

time_spec.rb

## Setup
require 'dry/effects'

RSpec.configure do |config|
  config.include Dry::Effects::Handler.CurrentTime
  config.include Dry::Effects.CurrentTime

  config.around { |ex| with_current_time(&ex) }
end

## Change the time

it 'uses current time as a start' do
  subscription = create_subscription(...)
  expect(subscription.start_at).to eql(current_time)
end

it 'closes a subscription with current time' do
  future = current_time + 86_400
  closed_subscription = with_current_time(proc { future }) { close_subscription(subscription) }
  expect(closed_subscription.closed_at).to eql(future)
end

https://dry-rb.org/gems/dry-effects/0.1/effects/current_time/

This example is great and clear so I did not write my own
It shows connecting two effects, handling and reading the current time effect, and a simple Dependency Injection effect, which we will talk about later