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Here Be Dragons

Here be dragons is an Intellij/Android Studio plugin that let's you annotate your impure Java methods with the @SideEffect annotation and shows a little dragon icon in the gutter when you call them.

How the plugin works

Why would I want to do this?

When writing functional style code, isolating impure and pure functions becomes very important. This helps you visually identify which methods are impure when a bunch of methods are being called in a code block.

For a beginner friendly introduction to functional programming in Android, please checkout out my blog series.


Install the plugin

Download the plugin jar and select "Install Plugin From Disk" in IntelliJ's plugin preferences.

Add the annotation library

Add the jcenter repository to your gradle build file if it's not already present:

repositories {

Next, add the lib containing the @SideEffect annotation as a dependency:

dependencies {
    compile 'com.anupcowkur:here-be-dragons-annotation:1.0.1'


Simpy add the @SideEffect annotation to any method you want like this:

import com.anupcowkur.herebedragons.SideEffect;

public class Test {
    public void foo() {
        // do some impure things

And when you call the method anywhere, you'll see the dragon icon show up in the IDE gutter.


This project is licensed under the MIT License

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