Kotlin Recipes: Code & SQL

Tap Run and the real output appears right under the code, so you know what it does before it goes into your project. No Kotlin to install, no IDE, no setup, no account.

390+ short examples, one task each. Over 95% run on Kotlin 2.4.

You know what you need, but not the exact syntax:
• How do I fall back to a default value when a variable is null?
• How do I return two values from a function?
• How do I merge two maps?
Each has a working example here.

• 24 sections, including strings and dates, collections, nullable types, classes and interfaces, enums, generics, extension functions, lambdas, exception handling, regular expressions, multithreading, files, JSON and XML, algorithms, and design patterns.
• What changed from Kotlin 1.4 to 2.0, with before-and-after code: value classes, sealed interfaces, data objects and the improved smart casts in Kotlin 2.0.
• Reference, 320+ entries: keywords and standard library functions for strings, collections, files, and coroutines. Tap a word in the code to look it up.
• 200+ SQL queries: JOIN, GROUP BY, subqueries, window functions; more than half run on a practice database.
• Search looks inside the code: type joinToString to find every example that uses it.
• Edit an example and run your version, or write your own.
• Works on iPhone, iPad, and Mac.
• Everything except running code works offline.

Free version: 210+ Kotlin examples and 120+ SQL queries, the full reference, and 12 runs and 12 edits a day (Kotlin and SQL runs share one limit). Full version: all examples and queries, unlimited edits and examples of your own, and up to 30 Kotlin and 80 SQL runs a day. One-time purchase, no subscription.

Built by a developer for developers. The project behind it has been in active development since 2015.