PHP Dependency Injection With Pimple

Injecting dependencies to our core application is an everyday requirements/needs and thus is a most commonly used design patterns. Composer already made our live easier by managing library dependencies for PHP applications. Today, I will introduce you with the best way of PHP dependency injection into a web application with using very simple and slim Pimple library. This article might rather be treated as tip/tricks better than a tutorial.

Lets Start With A Simple Approach:

Now, what about initiating various object instances that we will be using on our project? yes, sure we may do this by simply initiating all required objects in a bootstrap file and save them in a global variable and use from there wherever needed, such as below:

$libs = array();
$libs["cache"] =  new CacheObject();
$libs["orm"] =  new ORM();
$libs["logger"] =  new Logger();
//....so on

What Is The Problem With This Implementation?

Well, apparently nothing. But, the problems come along the way, when we are developing a comparatively larger application which manages a lot of dependencies, but not all requests use all dependencies. As you can notice, the above approach will initiate all dependencies unnecessarily even if they doesn’t need to. This will result higher memory consumption on server and also request processing performance impact as well.

Can’t Lazy Loading Already solved this?

If you know about lazy loading with PHP closure, then you will might wonder why we need another library when we can already do it. Yes, its true, its possible to do it without this library, but this library will just simplify the usage one step more along with other features. Such as, to use a lazy loaded object with that approach, you will have to write as below:

$log = $app["logger"]();
$log->addMessage("DEBUG", "Test Log message");

but if the initialization was with using Pimple, we could simple use

$app["logger"]->addMessage("DEBUG", "Test Log message");

Why Use Pimple For PHP Dependency Injection?

I will recommend using pimple because it is made to make the above process super simple and easy to use. To use pimple, you won’t have to do much, but in return you will get several things done:

$libs = Pimple();
$libs["cache"] = function() {  return new CacheObject();};
$libs["orm"] =  function() {  return new ORM();};
$libs["logger"] =  function() {  return new Logger();};
//....so on

That’s It?

Not really, there are some other useful features as well.

with using protect() method, you can tell pimple to define the anonymous function as parameter value instead of usual service definition.

Also, generally pimple if made to return the same instance. To change the behavior, if you want factory like behavior, it provides factory() method to wrap around the anonymous function and do the job.

Read the official documentation, which shows the usage nicely with examples.

Hope this simple PHP dependency injection tips will help in some scenario. If you have any questions about any use cae/feedback, I will love to hear it. Happy coding 🙂