are accessible by Java classes outside of your module.Īs you can imagine, this is not great, especially if you’re migrating a codebase from Java to Kotlin and you’re making an extensive use of the internal keyword. In other words: your internal function, classes, interfaces, variables etc. Internal declarations in Kotlin are compiled to public declarations in Java. Unfortunately, there is no support for the internal modifier neither in Java nor in the bytecode. The internal modifier is handy when dealing with modularized projects, since it allows to easily contain the exposed API. If you’re not familiar with this modifier: it restricts the visibility of a declaration to the same module. Kotlin gave us a new visibility modifier: internal.

This is actually by design, but it’s worth noting when creating APIs that should be consumed by Java users. This is making the function that accepts an inline class impossible to use from Java. It’s interesting to note that the - char introduced by the mangling is an invalid character in Java. Public final void validate ( String password ) They are a great tool to easily create wrap types, without introducing runtime overheads due to type wrapping/unwrapping.Īn example could be a having Username/ Password inline classes to wrap String values. Inline Classes have been introduced as experimental in Kotlin 1.3. Let’s see two scenarios where name mangling is used inside the Kotlin compiler: inline classes and the internal modifier. This time I noticed that I was removing a method and adding a new one, and that was not expected, as it will result in a breaking change 🤨. Before releasing a new version of a library, I generally inspect the API surface to make sure I’m not introducing any unintended change to the API with a tool like japicmp. I discovered name mangling while preparing the release v3.1.0 of Chucker. This technique can be used to make identifiers harder to access in the bytecode. Name mangling is a technique used by the Kotlin Compiler to alter the name of identifiers (e.g. If you’ve played a bit around with Kotlin, chances are that you faced name mangling during your development. To destroy something by twisting it with force or tearing it into pieces so that its original form is completely changed.

Kotlin internal class meaning