Therefore, our functions work as expected. After the function invocation, we verify whether the corresponding element in the list gets updated or not. The block function we pass to each test case is updating the element in the list at a unique index. As the test function above shows, for simplicity, we’ve prepared a mutable list with nine elements. We want to test three functions and have three different test cases for each function: true, false, and null. Many thanks to Jake Wharton for helping with this article.Now, let’s write a test to verify whether our If-Then-Do functions work as expected: val aList = mutableListOf(0, 1, 2, 3, 4, 5, 6, 7, 8)ĭoIfTrue(true) assertThat(aList).isEqualTo(-1) It's succinct, efficient, easy-to-understand, and completely sidesteps any null checking whatsoever. In this case, the clear winner is groupingBy().eachCount(). Often times it depends on context for which strategy is best. Kotlin’s null safety segment can help developers get rid of NullPointerExceptions and some other common errors in writing qualitative codes, which direct to composing qualitative codes. (I don't mean to imply that this is an exhaustive list of strategies differing circumstances may yield more options.) Kotlin 101 stands for the first approach for Android app development here is the beginner guide to check out to build a robust Kotlin first application. Casting to non-null (with possible exception).I've demonstrated a number of strategies to convince the compiler that your code is okay:

Then we use the helper function Grouping.eachCount() to transform that into Map.Ĭollection-level operations can be incredibly powerful and are often more useful than iterating over collections manually (especially because the standard library can optimize what's going on behind the scenes). What we're doing here is first converting our List into a Grouping. Here's how we might try to write it: fun countInstances(list: List): Map. Suppose we want to convert a List into a Map, where each Int represents the number of times each String appeared in the list. Code that you know is ironclad turns out to be full of potential nulls. This null safety can occasionally create some tricky situations, though. Try to use a nullable type in a non-null way and the compiler will yell at you. One of the best features of Kotlin is its built-in null safety in the type system.

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