Initial commit

Author: Jonah

Gemfile

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+source 'https://rubygems.org'
+
+gemspec
+
+group :test do
+  gem 'rspec', '~> 3.8'
+end

LICENSE

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+MIT License
+
+Copyright (c) 2018 Jonah
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Install
+
+```
+gem install command_class
+```
+
+# Example Use
+
+1. Define your command object class.  This is a longish but real-worldish example:
+
+```ruby
+CreateUser = CommandClass.new(
+  dependencies: {user_repo: UserRepo, email_service: MyEmailService},
+  inputs: [:name, :email, :password]
+) do
+
+  def call
+    validate_input
+    ensure_unique_email
+    insert_user
+    send_confirmation
+  end
+
+  private
+
+  def validate_input
+    validate_name
+    validate_email
+    validate_password
+  end
+
+  def ensure_unique_email
+    email_exists = @user_repo.find_by_email(@email)
+    raise Errors::EmailAlreadyExists if email_exists
+  end
+
+  def insert_user
+    @user_repo.insert(name: @name, email: @email, password: @password)
+  end
+
+  def send_confirmation
+    @email_service.send_signup_confirmation(name: @name, email: @email)
+  end
+
+  def validate_name
+    valid = @name.size > 1
+    raise Errors::InvalidName unless valid
+  end
+
+  def validate_email
+    valid = @email =~ /@/
+    raise Errors::InvalidEmail unless valid
+  end
+
+  def validate_password
+    valid = @password.size > 5
+    raise Errors::InvalidPassword unless valid
+  end
+
+end
+```
+
+2. Create your command object itself:
+
+```ruby
+create_user = CreateUser.new
+```
+**NOTE:** Here, alternatively, we can inject dependencies other than the default ones, which vastly improves tests.  See the specs for examples of this.
+
+3. Run the command object:
+
+```ruby
+create_user.(name: valid_name, email: valid_email, password: valid_pw)
+```
+
+# Motivation
+
+On the benefits of Functional Command Objects:
+
+https://www.icelab.com.au/notes/functional-command-objects-in-ruby/
+
+For a more complex, but also more fully-featured version of this ideas, see:
+
+https://dry-rb.org/gems/dry-transaction/
+
+More to come...

command_class.gemspec

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+Gem::Specification.new do |s|
+  s.name        = 'command_class'
+  s.authors     = ['Jonah Goldstein']
+  s.homepage    = 'https://github.com/jonahx/command_class'
+  s.summary     = 'Create functional command objects without boilerplate'
+  s.version     = '0.0.1'
+  s.files       = ["lib/command_class.rb"]
+  s.test_files  = ["spec/command_class_spec.rb"]
+  s.license     = 'MIT'
+end

lib/command_class.rb

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+class CommandClass
+  def self.new(dependencies:, inputs:, &blk)
+    cmd_cls = Class.new
+    cmd_cls.const_set('DEFAULT_DEPS', dependencies)
+
+    cmd_cls.class_eval <<~RUBY
+      def initialize(**passed_deps)
+        deps = DEFAULT_DEPS.merge(passed_deps)
+        deps.each { |name, val| instance_variable_set('@' + name.to_s, val) }
+      end
+
+      def call(#{cmd_call_signature(inputs)})
+        Call.new(#{call_ctor_args(dependencies, inputs)}).()
+      end
+    RUBY
+
+    call_class = Class.new(cmd_cls, &blk)
+    call_class.class_eval <<~RUBY
+      def initialize(#{call_ctor_sig(dependencies, inputs)})
+        #{set_input_attrs(dependencies, inputs)}
+      end
+    RUBY
+
+    cmd_cls.const_set('Call', call_class)
+    cmd_cls
+  end
+
+  class << self
+
+    private
+
+    # TODO: allow for unnamed as well
+    def cmd_call_signature(inputs)
+      inputs.map {|x| "#{x}:" }.join(', ')
+    end
+
+    def set_input_attrs(deps, inputs)
+      all_args(deps, inputs).map {|x| "@#{x} = #{x}" }.join('; ')
+    end
+
+    def call_ctor_sig(deps, inputs)
+      all_args(deps, inputs).join(', ')
+    end
+
+    def call_ctor_args(deps, inputs)
+      [deps.keys.map { |x| "@#{x}" } + inputs].join(', ')
+    end
+
+    def all_args(deps, inputs)
+      deps.keys + inputs
+    end
+  end
+end

spec/command_class_spec.rb

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+require 'rspec'
+require_relative"../lib/command_class"
+
+# Setup classes and collaborators to test
+#
+UserRepo = Class.new
+MyEmailService = Class.new
+
+module Errors
+  class InvalidName < RuntimeError; end
+  class InvalidEmail < RuntimeError; end
+  class InvalidPassword < RuntimeError; end
+  class EmailAlreadyExists < RuntimeError; end
+end
+
+CreateUser = CommandClass.new(
+  dependencies: {user_repo: UserRepo, email_service: MyEmailService},
+  inputs: [:name, :email, :password]
+) do
+
+  def call
+    validate_input
+    ensure_unique_email
+    insert_user
+    send_confirmation
+  end
+
+  private
+
+  def validate_input
+    validate_name
+    validate_email
+    validate_password
+  end
+
+  def ensure_unique_email
+    email_exists = @user_repo.find_by_email(@email)
+    raise Errors::EmailAlreadyExists if email_exists
+  end
+
+  def insert_user
+    @user_repo.insert(name: @name, email: @email, password: @password)
+  end
+
+  def send_confirmation
+    @email_service.send_signup_confirmation(name: @name, email: @email)
+  end
+
+  def validate_name
+    valid = @name.size > 1
+    raise Errors::InvalidName unless valid
+  end
+
+  def validate_email
+    valid = @email =~ /@/
+    raise Errors::InvalidEmail unless valid
+  end
+
+  def validate_password
+    valid = @password.size > 5
+    raise Errors::InvalidPassword unless valid
+  end
+
+end
+
+# THE TESTS THEMSELVES
+#
+describe CommandClass do
+
+  context "full CreateUser example" do
+    let(:email_svc) { spy('email') }
+    let(:user_repo) { spy('user_repo') }
+    let(:valid_name) { 'John' }
+    let(:valid_email) { '[email protected]' }
+    let(:valid_pw) { 'secret' }
+
+    describe "happy path" do
+      let(:happy_repo) do
+        user_repo.tap do |x|
+          allow(x).to receive(:find_by_email).and_return(nil)
+        end
+      end 
+
+      subject(:create_user) do
+        CreateUser.new(user_repo: happy_repo, email_service: email_svc)
+      end
+
+      it 'inserts the user into the db' do
+        create_user.(name: valid_name, email: valid_email, password: valid_pw)
+        expect(user_repo).to have_received(:insert)
+      end
+
+      it 'sends the confirmation email' do
+        create_user.(name: valid_name, email: valid_email, password: valid_pw)
+        expect(email_svc).to have_received(:send_signup_confirmation)
+      end
+
+    end
+
+    describe "invalid user input" do
+      subject(:create_user) do
+        CreateUser.new(user_repo: user_repo, email_service: email_svc)
+      end
+
+      it 'errors for a short name' do
+        expect do
+          create_user.(name: 'x', email: valid_email, password: valid_pw)
+        end.to raise_error(Errors::InvalidName)
+      end
+
+      it 'errors on an invalid email' do
+        expect do
+          create_user.(name: valid_email, email: 'bad_email', password: valid_pw)
+        end.to raise_error(Errors::InvalidEmail)
+      end
+    end
+
+    describe "existing email" do
+      let(:repo_with_email) do
+        user_repo.tap do |x|
+          allow(x).to receive(:find_by_email).and_return('user obj')
+        end
+      end 
+
+      subject(:create_user) do
+        CreateUser.new(user_repo: repo_with_email, email_service: email_svc)
+      end
+
+      it 'errors' do
+        expect do
+          create_user.(name: valid_name, email: valid_email, password: valid_pw)
+        end.to raise_error(Errors::EmailAlreadyExists)
+      end
+    end
+  end
+
+end