dic to the limit – desymfonyday, barcelona 2014

deSymfonyDay Barcelona 2014

DIC To The Limit

Ronny López

ABOUT ME US

Hard way learner !Technical Lead at Social Point Do stuff at TangoTree in the nights !

@ronnyltwww.tangotree.iohttps://github.com/ronnylt

http://www.tangotree.io

https://github.com/ronnylt

AGENDA

• The problems

• Dependency Injection

• Coupling done right

• Dependency Inversion Principle

• Types of DI

• Dependency Injection Containers

• Symfony Dependency Injection Container

• Interchangeable Services

THE PROBLEMS

• We require to switch out data access layer without compromising all the other parts of the application

• We need to use different implementations in different deployments (dragon game, monster game, etc…)

• We wish to deploy the application in different environments (testing, integration, staging, production, etc…)

• We need different configurations in each environment

YAGNI You aren't gonna need it, let’s go home!

IN CASE YOU NEED IT

• You have to do Dependency Injection, correctly

• You have to know and apply Dependency Inversion Principles

WHAT WE REALLY WANT IS

• Code that is easy to test

• Clear separation of infrastructure logic from application logic

• Interchangeable infrastructure

WHY?

• Multiple deployments share parts of the same code, but each deployment has specific infrastructure needs

• Multiple environments with different needs

• We want to automatically test all the things

• We want to go fast, and the only way to go fast is… you know…

“The only way to go fast, is to go

well”

Uncle Bob

DEPENDENCY INJECTION

Dependency injection is a simple way to decouple classes from what they

depend on

Dependency injection decouples classes

construction from the construction of it’s

dependencies

IS IT ALL ABOUT COUPLING?

COUPLING

Mod A Mod B

Mod C Mod D

Tight (high, strong)

Mod A Mod B

Mod C Mod D

Loose (low, weak)

Mod A Mod B

Mod C Mod D

None

Coupling is a measure of the independency of components/modules

COUPLING

• The history of software shows that coupling is bad, but it also suggest that coupling is unavoidable

• An absolutely decoupled application is useless because it adds no value

• Developers can only add value by coupling things together

COUPLING DONE RIGHT

• Components make no assumptions about what other components do, but rely on their contracts

• Use an interface to define a type and focus on what is important

• Concrete implementations of the interfaces should be be instantiated outside the component

DEPENDENCY INVERSION PRINCIPLE

High-level modules should not depend on low-level

modules. Both should depend on

abstractions

Abstractions should not depend on details.

Details should depend on abstractions

DEPENDENCY INVERSION

• Decouple high level parts of the system from low level parts by using interfaces

OrderProcessor OrderRepository

MySqlOrderRepository

CassandraOrderRepository

LockSystem

RedisLockSystem

ZooKeeperLockSystem

<<interface>>

<<interface>>

ObjectStore RedisStorageDriver

InMemoryStorageDriver

RiakStorageDriver

StorageDriver<<interface>>

TYPES OF DEPENDENCY INJECTIONS

!

TYPES OF DI

• Constructor Injection

• Setter Injection

• Interface Injection

• Property Injection

• Service Locator

CONSTRUCTOR INJECTION

• Injects the dependencies via constructor

• It ensures that the choice of dependency is immutable

!class EnergyBuyCommandHandler implements CommandHandler!{! private $playerRepository;!! private $configRepository;!! public function __construct(!! ! PlayerRepository $playerRepository, !! ! ConfigRepository $config!! )! {! $this->playerRepository = $playerRepository;! $this->configRepository = $config;! }!}!


• It ensures that the choice of dependency is immutable

• The constructor is only ever called once when the object is created, so you can be sure that the dependency will not change during the object's lifetime

Pros Cons

• It is not suitable for working with optional dependencies

• Difficult to use in combination with class hierarchies


• Try to always use constructor injection

• If dealing with legacy code that does not support it, consider using an adapter class with constructor injection

• Depends on abstractions (interfaces), not concrete implementations

TIPS

SETTER INJECTION

• Inject the dependencies via a setter method

• The “injector” has to call the method in order to inject the dependency

!class LoggerChain implements SQLLogger!{! private $loggers = array();!! public function setLogger(SQLLogger $logger)! {! $this->logger = $logger;! }!}!

SETTER INJECTION

• Works “well” with optional dependenciesIf you do not need the dependency, then just do not call the setter

• You can call the setter multiple times.This is particularly useful if the method adds the dependency to a collection

Pros Cons

• Works “well” with optional dependencies Are you sure you need optional dependencies?

• You can call the setter multiple times

• You are not sure if the dependency was set

SETTER INJECTIONTIPS

• Avoid setter injections (the choice of dependencies is not inmutable)

• If you do Dependency Inversion right, probably YANGI

• Remember, your classes depend on abstractions, not concrete implementations, so you can use Null or Dummy implementations when necessary

SETTER INJECTIONEXAMPLE

use Psr\Log\LoggerInterface;!!final class OrderProcessor!{! private $logger;!! function __construct(. . ., LoggerInterface $logger)! {! $this->logger = $logger;! }!}!!final class GoodManLogger implements LoggerInterface {…}!!final class LogstarLogger implements LoggerInterface {…}!!final class NullLogger implements LoggerInterface {…}!

Instead of having a setter method to inject the logger, use constructor injection and use the appropriate logger implementation in each case

INTERFACE INJECTION

• Define and use interfaces for the injection

• Allows certain objects to be injected into other objects, that implement a common interface

• It’s a kind of setter injection, so same pros and cons

interface ContainerAwareInterface!{! public function setContainer(ContainerInterface $container = null);!}!!class ContainerAwareEventDispatcher implements ContainerAwareInterface!{! public function setContainer(ContainerInterface $container = null)! {! }!}!

PROPERTY INJECTION

• Allows setting public fields of the class directly

• There are mainly only disadvantages to using property injection, it is similar to setter injection but with additional important problems

!!class NewsletterManager!{! public $mailer;!! // ...!}!

PROPERTY INJECTION

• Useful if you are working with code that is out of your control, such as in a 3rd party library, which uses public properties for its dependencies

Pros Cons

• You cannot control when the dependency is set at all, it can be changed at any point in the object's lifetime

• You cannot use type hinting so you cannot be sure what dependency is injected except by writing into the class code to explicitly test the class instance before using it

SERVICES LOCATOR

• Is an object that knows how to get all of the services that an another service might need

interface CommandHandlerLocator !{! public function locate($commandName);!}!!!class ContainerCommandHandlerLocator implements CommandHandlerLocator!{! private $container;!! public function __construct(ContainerInterface $container)! {! $this->container = $container;! }!! public function locate($commandName)! {! if (!$this->container->has($commandName)) {! throw new NotFoundException('Unable to find command handler');! }!! return $this->container->get($commandName);! }!}!

SERVICE LOCATOR

• It’s easy to use and abuse due to its straightforward behaviour

• Not all use cases are bad, for example when you want to load services on demand at runtime

Pros Cons

• It hides dependencies in your code making them difficult to figure out and potentially leads to errors that only manifest themselves at runtime

• It becomes unclear what are the dependencies of a given class

• It’s easy to abuse

• It’s consider and anti-pattern (but there are valid use cases for it)

SERVICE LOCATORTIPS

• Use a segregated interface for the locator, do not depends on the whole locator (container)

!

• Limit the types of services a locator provides

DEPENDENCY INJECTION CONTAINER

Dependency Injection Container is simply an object that manages the

instantiation of other objects

Automagically creates a given type with all the required dependencies

DIC

• Most of the time you do not need a DIC to benefit from Dependency Injection

• But… creating and maintaining the dependencies by hand can become a nightmare pretty fast

• A DIC manages objects from their instantiation to their configuration

• The objects themselves should not know that they are managed by a container and should not know nothing about it

DEPENDENCY INJECTION CONTAINERS IN PHP

PHP DIC IMPLEMENTATIONS

• Twittee

• Pimple

• Illuminate\Di

• Zend\Di

• Symfony\DependencyInjection

• http://php-di.org/

• Build your own

SYMFONY DEPENDENCY

INJECTION CONTAINER

The Dependency Injection component allows you to standardize and centralize

the way objects are constructed in a SF

application

HOW IT WORKS?

• Reads definition of how objects (services) should be constructed (XML, YAML, PHP, etc…)

• Collects all definitions and builds a container

• When requested, creates objects and injects the dependencies

ADVANCED

HOW IT WORKS

• Compiler Passes

• Container Extensions

• Services Configurator

• Tagged Services

SYMFONY DIC

• Basic (and advances) usages are well documented in the Symfony official documentation

• Probably you are comfortable creating your own objects via the container

• So, let’s try to solve the problems we stated at the beginning

INTERCHANGEABLE SERVICES

OrderProcessor OrderRepository



LockSystem

RedisLockSystem

ZooKeeperLockSystem

<<interface>>

<<interface>>

ObjectStore RedisStorageDriver


RiakStorageDriver

StorageDriver<<interface>>

final class OrderProcessor!{! private $orderRepository;! private $lockSystem;! private $objectStore;!! function __construct(!! ! OrderRepository $repository, !! ! LockSystem $lockSystem, !! ! ObjectStore $objectStore)! {! $this->orderRepository = $repository;! $this->lockSystem = $lockSystem;! $this->objectStore = $objectStore;! }!}!!final class ObjectStore!{! function __construct(StorageDriver $driver)! {! }!}!!

!interface StorageDriver !{}!!final class RiakStorageDriver implements StorageDriver!{}!!final class RedisStorageDriver implements StorageDriver!{}!!final class InMemoryStorageDriver implements StorageDriver!{}!

!interface LockSystem !{}!!final class RedisLockSystem implements LockSystem!{}!!final class ZooKeeperLockSystem implements LockSystem!{}!

interface OrderRepository {}!!final class MySqlOrderRepository implements OrderRepository!{}!!final class CassandralOrderRepository implements OrderRepository!{}!

services:!! order_processor:!! ! class: OrderProcessor! arguments:!! ! ! object_store: @object_store!! ! ! order_repository: [mysql|cassandra] !! ! ! lock_system: [redis|zookeeper]!! ! ! !!! object_store:!! ! class: ObjectStore!! ! arguments:!! ! storage_driver: [riak|redis|inmemory]!



RedisLockSystem

ZooKeeperLockSystem

RedisStorageDriver


RiakStorageDriver

THE PROBLEM

• It’s not possible to decide in advance what concrete implementation a deployment or environment is going to use

• We must configure dependencies for all the concrete implementations and each one has their own dependencies

SERVICES SETUP

Deployment Environment Concrete Implementation

DRAGON TESTING in-memory

DRAGON STAGING/QA redis

DRAGON PROD mysql

MONSTER TESTING in-memory

MONSTER PROD cassandra

SOLUTIONS

1. Loading different configurations depending on the environment and aliasing services

2. Using synthetic services and aliases

3. Managing semantic configuration with extensions

4. Using a custom injector

1- LOADING DIFFERENT CONFIGURATIONS

Load different configurations depending on the kernel.environment

• Probably easy to setup for testing/dummy services

Pros Cons

• The choice is coupled to the environment

• All services get defined, even when you are not going to use them

!namespace Acme\DemoBundle\DependencyInjection;!!use Symfony\Component\DependencyInjection\ContainerBuilder;!use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;!use Symfony\Component\HttpKernel\DependencyInjection\Extension;!use Symfony\Component\Config\FileLocator;!!class AcmeDemoExtension extends Extension!{! public function load(array $configs, ContainerBuilder $container)! {! $loader = new YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));! $loader->load('services.yml');!! if ($this->container->getParameter('kernel.environment') == 'test') {! $loader->load('services_test.yml');! }! }!! public function getAlias()! {! return 'acme_demo';! }!}!

services:! storage_driver:! alias: storage_driver.riak!! storage_driver.riak:! class: RiakStorageDriver!! storage_driver.redis:! class: RedisStorageDriver!! storage_driver.memory:! class: InMemoryStorageDriver

!services:! storage_driver:! alias: storage_driver.memory!

services.yml services_test.yml

The choice is coupled to the environment

2- USING SYNTHETIC SERVICES AND ALIAS

Define abstraction as “synthetic” services

• Probably easy to setup for testing/dummy services

Pros Cons

• All services get defined, even when you are not going to use them

• You have to define dependencies of services you probably not are going to use

!namespace Acme\DemoBundle\DependencyInjection;!!use Symfony\Component\DependencyInjection\ContainerBuilder;!use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;!use Symfony\Component\HttpKernel\DependencyInjection\Extension;!use Symfony\Component\Config\FileLocator;!!class AcmeDemoExtension extends Extension!{! public function load(array $configs, ContainerBuilder $container)! {! $loader = new YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));! $loader->load('services.yml');! }!! public function getAlias()! {! return 'acme_demo';! }!}!

services:! storage_driver:! synthetic: true!! storage_driver.riak:! class: RiakStorageDriver!! storage_driver.redis:! class: RedisStorageDriver!! storage_driver.memory:! class: InMemoryStorageDriver!

!services:! storage_driver:! alias: storage_driver.redis!

services.yml app/config/config.yml

!services:! storage_driver:! alias: storage_driver.memory!

app/config/config_test.yml

3- MANAGING SEMANTIC CONFIGURATIONS WITH EXTENSIONS

• Instead of having the user override individual parameters, you let the user configure just a few, specifically created options.

• As the bundle developer, you then parse through that configuration and load services inside an “Extension"

• With this method, you won't need to import any configuration resources from your main application configuration: the Extension class can handle all of this


• Good fit if you are building a bundle to be used by 3rd parties and you have a lot of configuration options you want to validate

• Lot of boilerplate code

• Extra complexity added

• You just wanted to manage dependency injection right?

class Configuration implements ConfigurationInterface!{! protected function addObjectStoreSection(ArrayNodeDefinition $rootNode)! {! $rootNode! ->children()! ->arrayNode('object_store')! ->isRequired()! ->children()! ->arrayNode('store_driver')! ->children()! ->scalarNode('type')->isRequired()->end()! ->scalarNode('connection')->end()! ->scalarNode('create_buckets')->end()! ->end()! ->validate()! ->ifTrue(function ($v) {! switch ($v['type']) {! case 'doctrine_dbal':! if (!isset($v['connection']) ||! !isset($v['create_buckets'])) {! return true;! }! break;! }!! return false;! })! ->thenInvalid('children configuration')! ->end()! ->isRequired()! ->end()! ->end()! ->end();! }!}

!$definition = $container->getDefinition($storageDriver);!switch ($config['storage_driver']['type']) {! case 'doctrine_dbal':! $definition->replaceArgument(0, new Reference($config['storage_driver']['connection']));! $definition->replaceArgument(1, $config['storage_driver']['create_buckets']);! break;! case 'redis':! $definition->replaceArgument(0, new Reference($config['storage_driver']['connection']));! break;!}!!$container->setAlias('object_storage.driver', $storageDriver);!

Configuration

Extension


• More powerful than simply defining parameters: a specific option value might trigger the creation of many service definitions;

• Ability to have configuration hierarchy

• Smart merging of several config files (e.g. config_dev.yml and config.yml)

Pros Cons

• Too much verbose, a lot of boilerplate code

• Extra complexity added if you only want to define dependencies and not a long configuration tree

!

4- USING A CUSTOM INJECTOR

• Let’s forget the Symfony DIC for a moment

• Let’s go back to dependency management problem again




RedisLockSystem

ZooKeeperLockSystem

RedisStorageDriver


RiakStorageDriver

“A good architecture allows you to defer critical decisions, it doesn’t force you to defer

them. However, if you can defer

them, it means you have lots of flexibility”

!

Uncle Bob

“A good architecture allows volatile decisions to be easily

changed” !

Uncle Bob




RedisLockSystem

ZooKeeperLockSystem

RedisStorageDriver


RiakStorageDriver

We need a dependency injection tool that allow us to easily change

volatile decisions

We need a dependency injection tool that allow us to defer critical

decisions

Core Framework

Payment Component

Analytics Component

Object Store Lock System

Component Exports Depends On

Unit Of Work Storage Driver

Order Processor Product Repository

Order Repository

Payment Gateway

Tracker Tracker Queue

Implementations

Redis, Zookeper

Redis, C*, Riak, MySql

Config, API

MySql, C*

Itunes, Facebook, Amazon, Google

Play

Redis, RabbitMQ, SQS, Kinesis

Core Component Object Store Lock System

Component Exports Depends On

Unit Of Work Storage Driver

Implementations

Redis, Zookeper

Redis, C*, Riak, MySql

namespace SP\Core\Game\Framework;!!class FrameworkComponent implements Component!{! public function getName()! {! return 'core.game.framework';! }!! public function getServicesDefinition()! {! return ServicesDefinition::create()!! ->dependsOn('storage_driver')! ->withInstanceOf('SP\Core\Component\ObjectStore\Storage\StorageDriver')!! ->dependsOn('lock_system')! ->withInstanceOf('SP\Core\Component\Lock\LockSystem')!! ->exports('object_store')! ->withClass('SP\Core\Component\ObjectStore')! ->andConstructorDependencies(‘storage_driver’, ‘lock_system’);! }!}

These are the decisions the component developer wants to defer

Depends on abstractions, not concrete implementations

Payment Component Order Processor Product Repository

Order Repository

Config, API

MySql, C*

namespace SP\Core\Game\Payment;!!class PaymentComponent implements Component!{! public function getName()! {! return 'core.game.payment';! }!! public function getServicesDefinition()! {! return ServicesDefinition::create()!!! ! ! ->dependsOn('product_repository')! ->withInstanceOf('SP\Core\Game\Payment\Product\Repository\ProductRepository')!! ->dependsOn('order_repository')! ->withInstanceOf('SP\Core\Game\Payment\Order\Repository\OrderRepository')!! ->dependsOn('gateways')! ->withInstanceOf('GatewayDefinition')!! ->exports(‘order_processor')! ->withClass('SP\Core\Game\Payment\OrderProcessor')! ->andConstructorDependencies(‘gateways', ‘product_repository’, ‘order_repository’);! }!}

Itunes, Facebook, Amazon, Google

Play

Payment Gateway

These are the decisions the component developer wants to defer

Depends on abstractions, not concrete implementations

WHERE DOES THE MAGIC COME FROM?

• There is not such “magic”

• Each component define it’s dependencies in a easy and legible way

• Framework agnostic dependency definition

• Based on the dependency definitions, services are added to the container during the container building phase

HOW?

• First, collect services definitions from installed components

• Second, inject services definitions into the Symfony (or Silex, or…) container

• No magic, just code !!!

USING SYMFONY

• Collect services definitions from installed components

• Inject services definitions into the Symfony (or Silex, or…) container

use Symfony\Component\DependencyInjection as DI;!!!final class ComponentDependencyInjector implements DI\Compiler\CompilerPassInterface!{! private $components;!! public function __construct(array $components = array())! {! $this->components = $components;! }!! public function process(ContainerBuilder $container)! {! foreach ($this->components as $component) {! $services = $component->getServicesDefinition();! foreach ($services->dependencies as $definition) {! $id = $component->getName() . '.' . $definition->name;!! if (!$container->has($id)) {! throw new ServiceNotFoundException($component->getName(), $id, $definition->instanceOf);! }! }! }! }!! public function registerComponentsDependencies(ContainerBuilder $container)! {! foreach ($this->components as $component) {! $this->addComponentDependencies($container, $component);! }! }!! private function addComponentDependencies(ContainerBuilder $container, Component $component)! {! $container->addObjectResource($component);! $services = $component->getServicesDefinition();! foreach ($services->exports as $definition) {! $this->addDefinition($container, $definition, $component);! }! foreach ($services->definitions as $definition) {! $this->addDefinition($container, $definition, $component);! }! }!! $def = new DI\Definition($definition->class, $args);! $def->setPublic($definition->public);!! $container->setDefinition($component->getName() . '.' . $definition->name, $def);! }!}!

The Component Dependency Injector responsibility is to inject the definitions in a given container

use Symfony\Component\HttpKernel\Kernel;!use Symfony\Component\Config\Loader\LoaderInterface;!!class AppKernel extends Kernel!{! public function registerBundles()! {! $bundles = array(! new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),! new Symfony\Bundle\MonologBundle\MonologBundle(),!! new SP\Core\Bundle\GameFrameworkBundle\GameFrameworkBundle([! new \SP\Core\Game\Framework\FrameworkComponent(),! new \SP\Core\Game\Framework\PaymentComponent(),! new \SP\Core\Game\Framework\AnalyticsComponent(),! ]),! );! }!}!

The AppKernel

These are the framework agnostic components that provide infrastructure and logic for the application

namespace SP\Core\Bundle\GameFrameworkBundle;!!use Symfony\Component\DependencyInjection\Compiler\PassConfig;!use Symfony\Component\HttpKernel\Bundle\Bundle;!use Symfony\Component\DependencyInjection\ContainerBuilder;!!use SP\Core\Bridge\Symfony\DependencyInjection\ComponentDependencyInjector;!!class GameFrameworkBundle extends Bundle!{! private $components;!! function __construct(array $components = array())! {! $this->components = $components;! }!! public function build(ContainerBuilder $container)! {! $injector = new ComponentDependencyInjector($this->components);! $injector->registerComponentsDependencies($container);!! $container->addCompilerPass($injector, PassConfig::TYPE_BEFORE_REMOVING);! }!}!

The (in)Famous Framework Bundle

The components we are “installing” in this application

The “magic” is here !!!

[SP\Core\Bridge\Symfony\DependencyInjection\Exception\ServiceNotFoundException] Component "core.game.framework" requires the service "core.game.framework.lock_system" as an implementation of "SP\Core\Component\Lock\LockSystem" but the service is not defined.

[SP\Core\Bridge\Symfony\DependencyInjection\Exception\ServiceNotFoundException] Component "core.game.payment" requires the service “core.game.payment.product_repository” as an implementation of "ProductRepository" but the service is not defined.

$ php app/console

The application complains about missing dependencies required by installed components

We are planning to add suggested implementations for this requirement

services:!!! core.game.framework.lock_system:!! ! public: false!! ! class: SP\Core\Component\Lock\RedisLockSystem!! ! arguments:! redis: @sp.core.redis.connector.lock! timeout: 10! expiration: 10!

config.yml

services:!!! core.game.framework.lock_system:!! ! public: false!! ! class: SP\Core\Component\Lock\MemoryLockSystem!! ! arguments:! timeout: 10! expiration: 10!

config_test.yml

The application config Concrete implementation in the application (by default)

Semantic configuration?

Concrete implementation in the application (test mode)

4- USING A CUSTOM INJECTOR

• Complete control of component dependencies

• Very limited in features (only constructor injections allowed)

• Framework agnostic

• Allows you to defer critical and volatile decisions

Pros Cons

• Very limited in features (only constructor injections allowed)

!

!

CONCLUSIONS

• You have the tools, use the best tool that solve your problems

• Don’t be afraid of going to the limit with the framework you use

• The framework is just an implementation detail

SOME REFERENCES

http://www.objectmentor.com/resources/articles/dip.pdf !http://www.martinfowler.com/articles/injection.html !http://martinfowler.com/articles/dipInTheWild.html !http://desymfony.com/ponencia/2013/inyeccion-dependencias-aplicaciones-php !http://fabien.potencier.org/article/11/what-is-dependency-injection !http://fabien.potencier.org/article/12/do-you-need-a-dependency-injection-container !http://fabien.potencier.org/article/13/introduction-to-the-symfony-service-container !https://www.youtube.com/watch?v=IKD2-MAkXyQ !http://richardmiller.co.uk/2014/03/12/avoiding-setter-injection/ !http://richardmiller.co.uk/2014/03/28/symfony2-configuring-different-services-for-different-environments/ !http://www.infoq.com/news/2013/07/architecture_intent_frameworks !http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html !

http://www.objectmentor.com/resources/articles/dip.pdf

http://www.martinfowler.com/articles/injection.html

http://martinfowler.com/articles/dipInTheWild.html

http://desymfony.com/ponencia/2013/inyeccion-dependencias-aplicaciones-php

http://fabien.potencier.org/article/11/what-is-dependency-injection

http://fabien.potencier.org/article/12/do-you-need-a-dependency-injection-container

http://fabien.potencier.org/article/13/introduction-to-the-symfony-service-container

https://www.youtube.com/watch?v=IKD2-MAkXyQ

http://richardmiller.co.uk/2014/03/12/avoiding-setter-injection/

http://richardmiller.co.uk/2014/03/28/symfony2-configuring-different-services-for-different-environments/

http://www.infoq.com/news/2013/07/architecture_intent_frameworks

http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html

THANK YOUFor your attention

@ronnylt

dic to the limit – desymfonyday, barcelona 2014

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