snippet_1.rb

class CreateUser
  class Error < StandardError; end
  
  # ...
end

# contoller
begin
  user = CreateUser.new(params).call
  p "User #{user.username} created succesfully"
rescue CreateUser::Error => e
  p "Didn't work because #{e.to_s}"
end

snippet_10.rb

require 'dry/monads/result'
require 'dry/matcher/result_matcher'

class CreateUser
  include Dry::Monads::Result::Mixin
  include Dry::Matcher.for(:call, with: Dry::Matcher::ResultMatcher)

  def call(params)
    # Failure is a method for constructing the Failure object
    return Failure(message: 'smth') if smth_is_invalid?
    
    Success(user: user)
  end
end

create_user = CreateUser.new(other_service: OtherServce.new)
create_user.call(params) do |result|
  result.success do |user:|
    p "User #{user.username} created"
  end

  result.failure do |error_message:|
    p "Operation failed because of #{error_message}"
  end
end

snippet_2.rb

# contoller
begin
  user = CreateUser.new(params).call
  p "User #{user.username} created succesfully"
rescue ActiveRecord::RecordInvalid => e
  p "Didn't work because #{e.to_s}"
end

snippet_3.rb

# controller
if CreateUser.new(params).call
  p 'Operation succeeded
else
  p 'Operation failed
end

snippet_4.rb

# controller
create_user = CreateUser.new(params)
if create_user.call
  user = create_user.user
  p "User #{user.username} created"
else
  p "Operation failed because of #{create_user.error_message}"
end

snippet_5.rb

class CreateUser
  def self.call(params)
    new(params).call
  end

  def initialize(params)
    ...
  end
  
  def call
    ..
  end
end

snippet_6.rb

# controller
result = CreateUser.call(params)
if result.success?
  user = result.user
  ...

snippet_7.rb

# controller
result = CreateUser.run(params)
if result.success?
  user = result.user
  ...

snippet_8.rb

# controller
result = CreateUser.run(params.merge(other_service: OtherServce.new))
if result.success?
  ...

snippet_9.rb

# create_user.rb
class CreateUser
  # Define result objects.
  class Success < Hash; end
  class Failure < Hash; end
  
  def call(params)
    return Failure.new(message: 'smth') if smth_is_invalid?
    ....
    Success.new(user: user)
  end
end

# In controller, initialize the service using DI if needed.
create_user = CreateUser.new(other_service: OtherServce.new)
result = create_user.call(params)
if result.is_a? CreateUser::Success
  user = create_user[:user]
  p "User #{user.username} created"
else
  p "Operation failed because of #{result[:error_message]}"
end