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Zsolt Szend:
Dynamic dependency injection
May 18, 2016 @ 13:32:25

In this new tutorial Zsolt Szende talks about dependency injection and how to handle objects and related needs at runtime rather than the pre-configured method that some injection containers/systems have defined.

In this short article I would like to demonstrate a way to inject dependencies that are not known until runtime. There are many use cases for this and in essence it is about choosing between concrete implementations of some common interface. In object oriented design this is known at the Strategy pattern. The choice itself can be made in various ways, for example via a configuration option or a command line parameter in case of a console command, and I think the dynamic nature of the choice is the most interesting part of the pattern.

The article provides a practical example of an XML/JSON reader pulling information from an external source. A simple interface is defined and two implementation classes put it to use. Then the "command" pattern is used to apply it to an executable script and how injecting a reader type directly overrides the one from the provided option. This is taken a step further and refactored into a "resolver" to determine the best logic to apply based on the input argument.

tagged: dynamic dependency injection xml json reader tutorial resolver

Link: http://pwm.github.io/dynamic-dependency-injection/

QaFoo.com:
Never Use null
May 03, 2016 @ 13:07:32

On the QaFoo.com blog they've made a recommendation in their latest post - they suggest that you never use null.

When doing code reviews together with our customers we see a pattern regularly which I consider problematic in multiple regards – the usage of null as a valid property or return value. We can do better than this.

Let's go into common use cases first and then discuss how we can improve the code to make it more resilient against errors and make it simpler to use. Most issues highlighted are especially problematic when others are using your source code. As long as you are the only user (which hopefully is not the case) those patterns might be fine.

They talk about some of the most common uses they see for using null in PHP applications including setters for class properties (injection). They point out that in PHP 7 a missing value on a property would result in a Fatal error and make the functionality harder to test overall. They suggest that all required dependencies be injected on object construction instead, making it easier to know the current state of the object on testing. They also talk some about using null as a return value, how it could make debugging difficult and a solution that could make more sense - throwing an exception instead.

tagged: never use null return value injection setter solution suggestion debugging

Link: https://qafoo.com/blog/083_never_use_null.html

Rob Allen:
DI Factories for Slim controllers
Apr 28, 2016 @ 10:38:10

In a recent post to his site Rob Allen shows you how to create dependency injection factories for Slim (v3) controllers.

When using classes for route actions in Slim 3, I recommend using a single class for each route. However you can use a single class for multiple routes. To register a class method to a route you pass a string as the route callable where the class name is separate from method by a colon. Slim will retrieve MyController from the DI container and then call the listAction method using the usual signature. f you don't specify a method, then Slim will see if it treat the class as a callable, so you can implement __invoke() and then register the route.

He shows how to create a factory method as a part of the Slim container for a constructor and inject the correct dependencies. He shows how to register these dependencies as other factory methods inside the DI container and how to pull them back out for injection. He prefers this method as it reduces "hidden dependency" issues and makes the controllers themselves easier to test.

tagged: slim3 slimframework dependency injection container tutorial factory

Link: https://akrabat.com/di-factories-for-slim-controllers/

PHP-DI:
Introducing the PHP-DI bridge for Slim
Mar 11, 2016 @ 10:15:24

In this new article on the PHP-DI project site they've shared one of the latest tools they've created to make it easier to integrate PHP-DI with the latest version of the Slim microframework (v3).

Slim 3 was released 3 months ago and it was significant. It is one of the first frameworks to integrate the latest standards and concepts in its core.

[...] While PSR-7 and middlewares are very interesting, what's more useful for us is the use of container-interop. That means Slim 3 can work with any dependency injection container. It is very easy to replace the default container (Pimple) with PHP-DI, but today we are releasing a "PHP-DI - Slim" bridge that goes a little further.

They then show how to use their new bridge to create controllers as services in the container and pass them parameters. The post ends with the instructions on getting the PHP-DI bridge installed and how to use it to replace the default AppSlim creation of your application.

tagged: phpdi dependency injection container slim microframework slimframework v3 bridge

Link: http://php-di.org/news/18-slim-bridge-released.html

Loïc Faugeron:
The Ultimate Developer Guide to Symfony - Dependency Injection
Feb 25, 2016 @ 10:43:57

Loïc Faugeron has posted another of his "Ultimate Developer Guide" series to his site, this time with a focus on the dependency injection component of the Symfony framework.

In this guide we explore the standalone libraries (also known as "Components") provided by Symfony to help us build applications. We've already seen: HTTP Kernel and HTTP Foundation, event dispatcher, routing and YAML. We're now about to check Dependency Injection, and finally in the next article we'll have a look at Console.

He starts with an introduction to the dependency injection pattern by refactoring a request to an API for its status out into classes with different responsibilities. He includes both the code he started with and what he's refactoring to. He thing brings in the Dependency Injection component, shows how to register the different classes and define a YAML configuration with their relationships. He also includes an examples of how to pass in parameters when injecting services, extending the functionality and compile the functionality into static values.

tagged: ultimate developer guide symfony dependency injection tutorial series

Link: https://gnugat.github.io/2016/02/24/ultimate-symfony-dependency-injection.html

SitePoint PHP Blog:
How to Build Your Own Dependency Injection Container
Feb 12, 2016 @ 12:22:12

The SitePoint PHP blog has posted a tutorial showing you how to build something that's become an integral part of most frameworks and applications practicing modern PHP development: a dependency injection container.

A search for “dependency injection container” on packagist currently provides over 95 pages of results. It is safe to say that this particular “wheel” has been invented.

However, no chef ever learned to cook using only ready meals. Likewise, no developer ever learned programming using only “ready code”. In this article, we are going to learn how to make a simple dependency injection container package.

He walks you through the entire process of creating the container and each of the pieces that make it up:

  • the overall interface for the container (with has/get methods)
  • having it cooperate with the "container interoperability" structure
  • reference handling
  • constructor injection functionality

Code is included the whole way showing you how to create the parts and fit them together to make more of a whole. He ends the post with a look at a few other dependency injection containers and a reference to the repository with the end result of the article.

tagged: dependency injection container tutorial introduction

Link: http://www.sitepoint.com/how-to-build-your-own-dependency-injection-container/

Toptal.com:
True Dependency Injection with Symfony Components
Jan 20, 2016 @ 10:37:39

On the Toptal.com blog there's a recent post about true dependency injection with Symfony between components in your application and only using the dependency injection container for its intended purpose.

Symfony2, a high performance PHP framework, uses Dependency Injection Container pattern where components provide a dependency injection interface for the DI-container. This allows each component to not care about other dependencies. [...] But this means DI-container can be used as a Service Locator.

[...] In this article we will try to build a Symfony2 application without implementing Service Locator pattern. We will follow one simple rule: only DI-container builder can know about DI-container.

They start off by talking about the structure of the dependency injection container and how it relates to the three main types: controller, method and property injections. He then starts in on creating the sample project and requiring only the Symfony DI, configuration and Yaml components. He then creates a ContainerBuilder class and sets up the HttpKernel functionality to pull the response from the container. He then makes a simple controller with a default action that just responds with text. With this working he updates it to pull in an input variable. He then makes updates to the application with changes to the route handing, templating (Twig), Doctrine (database) and tag handling.

tagged: dependency injection di symfony component framework router yaml container tutorial httpkernel

Link: http://www.toptal.com/symfony/true-dependency-injection-symfony-components

Alejandro Celaya:
Improve DI in PHP apps with Zend Framework plugin managers
Jan 04, 2016 @ 11:40:39

In this new post to his site Alejandro Celaya offers some advice on improving the dependency injection of your application with the help of the Zend Framework plugin managers. More specifically he talks about the AbstractPluginManager, a part of the ZendServiceManager package.

Generally it is a very bad practice to inject a service container into any object, but there are some situations where it could be even good, when certain conditions are met.

In one of the ZF2 mailing lists somebody asked which were these situations. I couldn't find the email, but the answers said that you can do it when the service container manages resources of the same type, and your object virtually depends on all of them. [...] If you have another object that needs to perform database connections, you don't want to inject all of the connection objects into it, you should rather inject the connection pool. That will reduce the number of dependencies of your object.

In this situation, the connection pool is some kind of service container, but injecting it has more benefits than disadvantages.

He shows how to use the AbstractPluginManager to achieve this goal, noting the existence of a validatePlugin method that can be used to ensure all necessary dependencies are available. He includes a real example of it in use, creating a simple "social plugin manager" that verifies that the plugin provided is either a closure or instance of FilterInterface.

tagged: dependency injection di zendframework plugin manager tutorial abstractpluginmanager

Link: http://blog.alejandrocelaya.com/2015/12/31/improve-dependency-injection-in-php-apps-with-zend-framework-plugin-managers/

Sarfraz Ahmed:
Coding to Interface
Dec 29, 2015 @ 09:27:48

On his Code in PHP site *Sarfraz Ahmed * has a post talking about coding to interfaces, how its done and why he thinks it's an essential part of any application.

One of the nicest things you can add to your programming skills is coding to interface.

One of the nicest things you can add to your programming skills is coding to interface. One of the five principles of S.O.L.I.D is Dependency inversion principle which states: [...] High-level modules should not depend on low-level modules. Both should depend on abstractions [and] abstractions should not depend on details. Details should depend on abstractions.

He elaborates on this "pretty formal definition" with an example MySQL wrapper class used in a User class, making them tightly coupled to each other. He also points out the same with a `UserController. As a solution to this tight coupling problem, he suggests using dependency injection (inversion of control) to pass in instances of the classes rather than creating them internally. This still couples them, though a bit more loosely, so he suggests using an interface for the dependency instead of a concrete class. This way any number of potential classes could be passed in and the class internally knows how to use them.

tagged: code interface dependency injection ioc solid principles objectoriented coupling

Link: http://codeinphp.github.io/post/coding-to-interface/

Shameer C:
Automatic construction injection in Slim 3
Oct 20, 2015 @ 11:09:38

Shameer C has a post to his site showing you how to automatically inject values in constructors on Slim 3 based applications. This makes use of the inheritance of constructor parameter functionality the Aura.DI container makes available.

In the previous blog post we have discussed how to replace the default Pimple Container with Aura.DI in Slim framework 3. Aura.DI gives us more flexibility in terms of managing dependencies. We saw one most useful feature in Aura.DI, Inheritance of constructor parameters, that will help us to avoid repeating common parameters for Controllers and Models. In this article we will see another advantage of the same feature.

He gives an example of how, with the default DI container in Slim (Pimple) you have to make a new instance of a class manually each time you need it. He talks about how Slim 3 internally resolves controller classes (using a CallableResolver) and a small change that can be made to prevent you from needed to define every constructor into the DI container and allow for more dynamic handling.

tagged: automatic injection constructor callableresolver slim3 tutorial auradi dependencyinjection

Link: http://blog.shameerc.com/2015/10/automatic-construction-injection-in-slim-3