Creating a Dependency Injection (DI) Container

UpdatedOctober 8, 2021

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Creating a Dependency Injection (DI) Container

Thomas Portelange

A Web Developer based in Belgium, specialized in PHP & JS development

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Why create my own

To be honest, it wasn't really the plan. I found out devanych/di-container and I was really impressed by the simplicity of it. But there were a few things I wanted to improve.

First, I wanted the DI container to fit in one single class. In order to do that, I had to convert the Exceptions to anonymous classes extending the base PSR interface.

And then, there were a couple of other features I wanted to have:

Picking dependency by name if they returned the proper type

Allow overriding distinct parameters

Call methods after instantiation (not everything can be set in the constructor)

Actually, I managed to fit all that under 300 LOC so I'm quite happy with the result. Of course, it's not as featured as PHP-DI or the Symfony DI component, but if 300 LOC do the job, why use more?

What is a minimalist container?

I had a discussion today on Reddit about Capsule 3 that was recently released. The package shared a lot of my own goals:

No cache (because it shouldn't be necessary)

PHP configuration (no yml, special syntax, etc)

Predictable output (always return the same instance once loaded)

But there was one key difference: it uses a Definition object instead of a plain array. While this may seem like an improvement, it's not perfect in my opinion:

It makes the package more complicated than needed (and you need to test it)

At the end of the day, you end up passing "magic" key/values to the argument method anyway, so it's not like the definition object help you to pick the right value (at least, a real config object would allow typed settings).

So... arrays it is for me.

Creating a Dependency Injection (DI) Container

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More from this blog

A git diff with all changed and new unstaged files

Writing a Zero-Dependency CSV and XLSX Reader/Writer

Media Queries Level 5 are awesome

Modern tooltips

Using Dialog elements today

But what is a DI container exactly?

Why create my own

What is a minimalist container?

Conclusion

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More from this blog

But what is a DI container exactly?

Why create my own

What is a minimalist container?

Conclusion