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An early look at Dagger Reflect


When it comes to solving the Dependency Inversion principle, there is no better way then using annotations in the JVM world. However, generating code in compile time has some costs. For example the build time. And I believe this is the only thing dagger can't do well alone.

This is not a bye bye dagger post. This is mostly, obtaining the most out of Dagger.

To solve this problem, Dagger-Reflect was written. What this tool does, is basically moving Dagger a step forward, from code generation at compile time, to code generation at Runtime, which basically is what reflection does, overall.

To set up Dagger-Reflect is pretty easy. Just add these lines to your build.gradle (module app) file:

You can check the docs for full or partial configuration. One thing that doesn't go well with this configuration is repetitive code if you have a lot of modules. Yes, you have to do this in every module that you have dagger. Therefore, there is already a plugin which handles that, and requires only a small configuration from you. Just add these lines of code in your build.gradle (module project) file:

Another small step is to add dagger.reflect = true , in your gradle.properties and you are good to go.

The usage of Dagger-Reflect is pretty simple. Instead of DaggerMyAwesomeAppComponent.factory().create(this), you should add DaggerReflect.factory(MyAwesomeAppComponent.Factory::class.java).create(this).

Notes to keep in mind: 
1- Your component must have a builder or a factory.
2- If you have annotations like @Qualifier (in my case, I don't) must have the runtime policy @Retention(RUNTIME)
3 - Should apply the reflection for every component in your application (In my case I have only one component)

Here is the result for the build time:



For more components, the difference might be greater. Imagine with multi modules and a lot of components each.

Why and how?
Dagger doesn't really generate the dependencies at compile time. If we notice, instead of new instances coming out of the DaggerMyAwesomeAppComponent, it's just 2 methods:

Some words about Proguard: You should apply Proguard rules, when full reflection is applied. But I'm not yet in production using Dagger-Reflect because I think it's to early. The current version is still 0.1.0.

Conclusion
As a code generation at compile time fan, i just jumped to code generation at runtime fan. I'm really interested to know how this kind of projects work. I have already forked Dagger2 in github and I hope I find some free time to study how it is done.

Best of luck!  💪💪💪

Stavro Xhardha

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