Jason Lotito - Latest Comments

Re: Injectors: Dependency Injection with Traits

Sandro Keil — Fri, 20 Mar 2015 16:11:38 -0000

Alright, it comes from this tweet. Maybe you should add an info message at the top of this post. So other people see that this post is deprecated.

Re: Injectors: Dependency Injection with Traits

Jason Lotito — Fri, 20 Mar 2015 15:51:41 -0000

This article was written, iirc, after reading numerous others talking about DI and SL systems that are essentially: $foo->get('logger') and then using factories behind the scenes. Basically, you were using plain old strings, and there was no way to find out how the logger was created without knowing the entire system. I love my IDE, and if I can't ctrl+click my way to victory, there is something wrong. =)

I've wanted to revisit this approach and correct some things and better answer some of the criticisms, but the code base I work on day-to-day is still using PHP 5.3, so I haven't had the opportunity to really see how it works in a real system.

Re: Injectors: Dependency Injection with Traits

mrclay — Fri, 20 Mar 2015 15:24:52 -0000

Yeah, our service locator has all the downsides associated with the pattern. We came from almost all global functions so this is just an iteration while we slowly migrate towards DI.

Re: Injectors: Dependency Injection with Traits

Jason Lotito — Fri, 20 Mar 2015 14:59:10 -0000

> It looks like a workaround for a missing service locator?
Yes. The Traits could implement the factories themselves. As mentioned though, this is an old article, and here mostly for posterity. For some reason, there are a number of people commenting on it today. *shrug*

Re: Injectors: Dependency Injection with Traits

Jason Lotito — Fri, 20 Mar 2015 14:57:39 -0000

My issue with this implementation is the non-obvious dependency on session, and potentially anything that _elgg_services() could return.

Re: Injectors: Dependency Injection with Traits

Jason Lotito — Fri, 20 Mar 2015 14:49:24 -0000

Yep. It's an old article, and something I experimented with. Don't have the comments from the original article, where we discussed the same basic things. It's here mostly for posterity.

Re: Injectors: Dependency Injection with Traits

Sandro Keil — Fri, 20 Mar 2015 13:14:37 -0000

I don't like this approach. It looks like a workaround for a missing service locator? Please have a look at the service manager of zf2 and inject your dependencies and use factories. A Trait is not the solution in this case.

Re: Injectors: Dependency Injection with Traits

mrclay — Fri, 20 Mar 2015 13:14:34 -0000

In Elgg our SL is returned by a global function _elgg_services() and here's how we might use it: https://github.com/Elgg/Elg...

We hint the type of properties on it here: https://github.com/Elgg/Elg...

Re: Injectors: Dependency Injection with Traits

mrclay — Fri, 20 Mar 2015 13:10:34 -0000

While I agree, there are large applications not easily refactorable to remove all storage logic from entities. A service locator is better than nothing. (but agreed this is worse that SL)

Re: Injectors: Dependency Injection with Traits

mrclay — Fri, 20 Mar 2015 13:07:25 -0000

A step above this would be to use a service locator that can at least give you documented types by using (faux) properties/methods. E.g. See https://github.com/mrclay/P...

Ideally you'd use a capable DIC like PHP-DI that uses reflection to auto-assemble the dependencies you need when it constructs the object.

Re: Injectors: Dependency Injection with Traits

David Adams — Fri, 20 Mar 2015 12:24:02 -0000

This isn't dependency injection. It's service location of the worst kind. Your User does not need ANY those services inside of it, especially not hidden behind static service location. You should have services that operate on the user, Ex: $mailer->sendRegistrationEmail($user), $session->cache($user), $tracker->track($user). Shoving your entire application inside of your entities is going to become a big ball of mud very quickly.

Re: What I know about designing credit card forms

Vitaliy — Wed, 27 Nov 2013 09:13:55 -0000

Great post, Jason! As always, I enjoy reading your article man. Keep it up!

Re: How to get an invite to Forrst

Clara — Thu, 12 Sep 2013 05:33:38 -0000

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Re: How to get an invite to Forrst

Isaac — Fri, 24 May 2013 23:43:11 -0000

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Re: How to get an invite to Forrst

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Re: Injectors: Dependency Injection with Traits

Adrian Imfeld — Sun, 16 Dec 2012 05:42:07 -0000

I really like your approach because of the following:
- All dependencies are clearly visible from the class constructor.
- Specification of phpdoc return type to allow for auto-completion.
- The injector seems like a good place for additional service bootstrapping.
- It's a great use of traits (of which I haven't seen many good examples)

I just wanted to point out what I perceive as a major difference between this method and proper DI/IoC. To many experts, DI/IoC implies constructing the whole (service) object graph in one go, before the control flow of the application starts.

I'm interested to hear about the problems you ran into with your approach, if you find the time to elaborate! For example, I don't see how you could inject dependencies which have other dependencies. I imagine running into serious problems when using another injector trait inside of an injector trait..

Re: Injectors: Dependency Injection with Traits

Jason Lotito — Sat, 15 Dec 2012 14:03:51 -0000

I understand what you are saying, but I think there are subtle difference between this method and Service Locator. The DiC is actually not important. The traits, in essence, can return anything however they want. That they happen to us a Service Locator in this case is unimportant.

Also, because of the way traits are setup in classes, they are clearly defined in the interface. This, of course, assumes are you using a common pattern, which in my case is injectors. Regardless, it creates that clear interface (avoiding one of the problems presented by service locators).

The final difference between this method and service locators is that with SL, it's difficult to follow the code and see what's actually happening. With traits, it's not. Quite the reverse.

I should note that I've continued to move forward from this.

I have problems with this method, but not the same problem I have with a service locator. Regardless, it's a pattern I continue to explore.

Thanks for the additional reading.

Re: Injectors: Dependency Injection with Traits

Adrian Imfeld — Sat, 15 Dec 2012 11:08:15 -0000

It seems to me that you're using Service Location (in an elegant way!) here, not Dependency Injection. Proper Dependency Injection implies constructing the whole object graph from scratch outside of the application’s control flow and injecting objects using the DiC as an *external agent*. The DiC should not be used inside the classes as you use it in your injector traits. Here are some relevant resources:

- http://blog.astrumfutura.co...
- http://blog.ploeh.dk/2010/0...

Re: How to get an invite to Forrst

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Re: How to get an invite to Forrst

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Re: How to get an invite to Forrst

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Re: Injectors: Dependency Injection with Traits

Jason Lotito — Fri, 20 Jul 2012 14:24:08 -0000

Yeah, so as you said, you could just inject it into the Container for the test. You can also create Injectors for your Tests and include them over your normal injectors.

Either way works fine for testing purposes. That was one of the things I wanted to spell out in the article, but it had been sitting around so long, I figured I'd get the idea out.

Anyways, it's still testable, whether you use a Container or not.

Re: Injectors: Dependency Injection with Traits

Bruce Weirdan — Fri, 20 Jul 2012 10:18:20 -0000

So how would you go about testing that User class? I don't see how would you mock the config in this case, since your injector is actually hardcoded in the use statement and you cannot substitute it.

On the second thought it seems you're using it as a substitute for internal accessor that are common when you have DI style code without DIC:
protected function _db() { if (!isset($this->_db)) $this->_db = new Db;
return $this->_db;}public function __construct($db = null) { $this->_db = $db;}public function someMethod() { $record = $this->_db()->query("...")->fetchOne(); // ...}

Re: How to get an invite to Forrst

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