A hands-on tour of Kotlin's core language features — from string templates to sealed classes and smart casts — one short, focused exercise at a time.https://rsicarelli.com/en© 2026 Rodrigo Sicarelli — CC BY-NC 4.0 (https://creativecommons.org/licenses/by-nc/4.0/)https://rsicarelli.com/en/blog/kotlin-koans-br-ola-mundo/https://rsicarelli.com/en/blog/kotlin-koans-br-ola-mundo/Change the code so that the start function returns the string "OK".Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-argumentos-nomeados/https://rsicarelli.com/en/blog/kotlin-koans-br-argumentos-nomeados/Make the joinOptions() function return the list in JSON format (for example, [a, b, c]) by specifying only two arguments.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-argumentos-padrao/https://rsicarelli.com/en/blog/kotlin-koans-br-argumentos-padrao/Imagine you have several overloads of foo() in your favorite language. You can replace them all with a single function in Kotlin.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-strings-com-tres-aspas/https://rsicarelli.com/en/blog/kotlin-koans-br-strings-com-tres-aspas/Swap the trimIndent call for trimMargin, setting # as the prefix value, so the resulting string no longer contains the prefix character.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-modelos-de-string/https://rsicarelli.com/en/blog/kotlin-koans-br-modelos-de-string/The pattern below matches a date in the format 13.06.1992 (two digits, a dot, two digits, a dot, four digits):Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-tipos-anulaveis/https://rsicarelli.com/en/blog/kotlin-koans-br-tipos-anulaveis/Rewrite the following code so that it uses only a single if expression, and learn how Kotlin handles nullable types safely.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-tipo-nenhum-nothing/https://rsicarelli.com/en/blog/kotlin-koans-br-tipo-nenhum-nothing/Specify the Nothing return type for the failWithWrongAge function.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-lambdas/https://rsicarelli.com/en/blog/kotlin-koans-br-lambdas/Pass a lambda to the any function to check whether the collection contains an even number.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-classes-de-dados-data-classes/https://rsicarelli.com/en/blog/kotlin-koans-br-classes-de-dados-data-classes/Rewrite the following code in Kotlin, then add the data modifier. A beginner-friendly look at Kotlin classes and data classes.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-tipagem-inteligente/https://rsicarelli.com/en/blog/kotlin-koans-br-tipagem-inteligente/Rewrite the given code using Kotlin smart casts and the when expression.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-classes-seladas/https://rsicarelli.com/en/blog/kotlin-koans-br-classes-seladas/Reuse your solution from the previous task, but replace the interface with a sealed interface. That way you no longer need the else branch in the when expression.Thu, 07 Mar 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-alias-para-importacao-import-alias/https://rsicarelli.com/en/blog/kotlin-koans-br-alias-para-importacao-import-alias/When importing a class or function, you can give it a different name by adding as NewName after the import directive. This can be useful when…Sat, 06 Apr 2024 00:00:00 GMThttps://rsicarelli.com/en/blog/kotlin-koans-br-extension-functions-e-properties-funcoes-e-propriedades-estendidas/https://rsicarelli.com/en/blog/kotlin-koans-br-extension-functions-e-properties-funcoes-e-propriedades-estendidas/Implement the extension functions Int.r() and Pair.r() so they convert an Int and a Pair into a RationalNumber.Sat, 06 Apr 2024 00:00:00 GMT