FailFast module proof of concept. Inspired by Hanami::Interactor

fail_fast.rb

module FailFast
  class Success

    attr_reader :data, :error

    def initialize(data)
      @data = data
    end

    def success?
      true
    end

    def failure?
      false
    end
  end

  class Failure

    attr_reader :data, :error

    def initialize(error)
      @error = error
    end

    def success?
      false
    end

    def failure?
      true
    end
  end

  module Helpers
    def error(message)
      Failure.new(message)
    end

    def error!(message)
      throw :fail, error(message)
    end

    def fail!(result = false)
      throw :fail, result
    end

    def success(data)
      Success.new(data)
    end
  end

  def self.wrap(*method_names)
    Module.new do
      define_singleton_method :included do |base|
        proxy = Module.new do
          method_names.each do |m|
            define_method(m) do |*args|
              catch(:fail) do
                super(*args)
              end
            end
          end
        end

        base.include Helpers
        base.prepend proxy
      end
    end
  end

  def self.key_wrap(*method_names)
    Module.new do
      define_singleton_method :included do |base|
        proxy = Module.new do
          method_names.each do |m|
            define_method(m) do |*args, **kwargs|
              catch(:fail) do
                super(*args, **kwargs)
              end
            end
          end
        end

        base.include Helpers
        base.prepend proxy
      end
    end
  end

  def self.auto_wrap(*method_names)
    Module.new do
      define_singleton_method :included do |base|
        proxy = Module.new do
          method_names.each do |m|
            # We need to detect if method supports keyword arguments to provide
            # right parameters order when calling super() which doesn't support
            # implicit parameters passing in define_method.
            if base.instance_method(m).parameters.any? { |a| a[0] == :key }
              define_method(m) do |*args, **kwargs|
                catch(:fail) do
                  super(*args, **kwargs)
                end
              end
            else
              define_method(m) do |*args|
                catch(:fail) do
                  super(*args)
                end
              end
            end
          end
        end

        base.include Helpers
        base.prepend proxy
      end
    end
  end
end

test_example.rb

require_relative 'fail_fast'

class SomeOperation

  def call(error_level = 0)
    error! "Fatal error!" if error_level > 1
    if error_level > 0
      error "Warning!"
    else
      success "hello!"
    end
  end

  def keywords(error_level: 0)
    error! "Fatal error!" if error_level > 1
    if error_level > 0
      error "Warning!"
    else
      success "hello!"
    end
  end

  def plain(error_level = 0)
    if error_level > 1
      fail!
    elsif error_level > 0
      false
    else
      true
    end
  end

  # We need to include mdule after methods are loaded so we can introspect them
  include FailFast.auto_wrap :call, :keywords, :plain
end

service = SomeOperation.new

puts "(0) ================================="
result = service.call(0)
puts result # =>
puts result.success? # => true
puts result.error.inspect # => nil
puts result.data.inspect # => "hello!""

puts "(1) ================================="
result = service.call(1)
puts result # =>
puts result.success? # => false
puts result.error.inspect # => "Warning!"
puts result.data.inspect # => nil

puts "(2) ================================="
result = service.call(2)
puts result # =>
puts result.success? # => false
puts result.error.inspect # => "Fatal error!"
puts result.data.inspect # => nil

puts "(3) ================================="
result = service.keywords(error_level: 0)
puts result # =>
puts result.success? # => true
puts result.error.inspect # => nil
puts result.data.inspect # => "hello!""

puts "(4) ================================="
result = service.plain(0)
puts result # => true

puts "(6) ================================="
result = service.plain(1)
puts result # => false

puts "(7) ================================="
result = service.plain(2)
puts result # => false