Compiler Hinting with Kotlin Contracts

Kotlin’s built-in null-safety makes it easy for us to write code that’s less error-prone and less susceptible to the unwanted and unexpected NullpointerException at runtime. We can do a lot to make sure it doesn’t happen, but sometimes there’s no way around dealing with possible null-values. Kotlin is introducing Contracts in the upcoming 1.3 release (currently m2) in which we can use contracts to tell the compiler how a function behaves and what results are implied, so we can benefit from improved smart-casts.

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Let’s stay away from silver bullet claims

Apparently everybody’s  favourite JVM language beat Java in a recent code-smell contest. The Register reported on a paper by Bruno Gois Mateus and Matias Martinez who had carried out an extensive survey of the rate of Kotlin usage in recent open-source Android projects. Well, they’d have to be fairly recent, wouldn’t they. Using the Paprika tool to sniff out anti-patterns, they reached the not so surprising conclusion that the Kotlin code under scrutiny smelled a lot better than your average Android project in Java.

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Kotlin Release news: Kotlin 1.2.60, Kotlin 1.3 M1, Kotlin Native 0.8

Some good news coming from Jetbrains, who have been tirelessly working on expanding and improving Kotlin and the tools provided with it. In this post I’ll provide an overview of the latest news.

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Going functional and fullstack with Spring Fu and Kotlin

Spring Fu is an experimental Kotlin micro-framework that makes it easy to create lightweight Spring-powered applications with functional APIs instead of annotations. Fu is for functional API, but that’s also a wordplay with the -fu suffix which means skill, the chinese character which means “good luck” and the chinese poetry. Sébastien Deleuze announced this interesting new Micro framework on twitter:

One of the interesting features is that Spring Fu really allows you to develop the full stack using Kotlin by writing your Gradle build file and application code in Kotlin.

Josh Long has put up a great youtube video to get you started with Spring Fu:

The micro part for me is due to minimal reflection usage, no classpath scanning and no annotation processing. While this requires you to be a bit more explicit in the configuration, it boosts startup of you application significantly. For more details make sure to check out the project on github:

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Optional Kotlin

Last week I was working on a code base which had been partially converted from Java to Kotlin. The converted Java code base was making extensive use of java.util.Optional. The use of Optional might be helpful in situations where you want to be very explicit about the fact that a function or variable might be empty (null), to avoid java.lang.NullPointerExceptions.

But do you still need this in Kotlin? Continue reading

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