The by keyword sets up a "delegate": an object that will serve as an intermediary for your property.

Map works as a property delegate for val properties. You can use by to set up a Map as a property delegate for some property, as we have done here for something and somethingElse.

This might be useful in cases where other code is giving you the Map (e.g., some data parser) and you want to have more natural Kotlin code for accessing the data.

• the documentation
• Elements of Kotlin