October 2025
Intermediate to advanced
100 pages
2h 27m
English
Content preview from Kotlin Brain TeasersBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Discussion
This puzzle’s first line of code is an unfinished enum class declaration that’s missing its name and body. So why doesn’t the compiler reject it?
A class declaration doesn’t end at the first line break—it can span multiple lines, continuing until the compiler determines that it’s syntactically complete. The formatting makes it look like private is the start of a new declaration, but in fact, it’s the end of the first one and acts as our missing class name.
A class doesn’t require a body and doesn’t need to end with a final line break. That means enum class private is a complete and valid declaration that can be immediately followed by another class.
Out of Context
If you’ve written code in other programming languages, you might be used ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.