Resource Cleanup

Using try, catch and finally blocks for resource cleanup is tedious and error-prone. In fact, Kotlin has a library functions that could help us to manage cleanup for us.

As we know, finally clause cleans up resources regardless of how try block exits. But what if an exception can happen while closing the finally clause. On top of that, if one exception is thrown inside a try and another while closing the resource, the latter shouldn’t conceal the former. Ensuring proper cleanup becomes very messy.

To reduce this complexity, Kotlin’s use() guarantees proper cleanup of closable resources, liberating you from handwritten cleanup code. use() rethrows all exceptions, so we must still deal with those exceptions.

We can find use() in Java documentation for AutoClosable. For example, to read lines from a File we apply use() to a BufferedReader.

fun main() {
  DataFile("test.txt")
    .bufferedReader()
    .use { it.readLines().first() }
}

use() ensures resource cleanup at the point the resource is created, rather than forcing us to write cleanup code when we are finished with the resource.