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Scoped resource usage

This material was written by Aasmund Eldhuset; it is owned by Khan Academy and is licensed for use under CC BY-NC-SA 3.0 US. Please note that this is not a part of Khan Academy's official product offering.

Kotlin does not have Python's resource managers or Java's try-with-resources, but thanks to extension functions, there's use:

File("/home/aasmund/test.txt").inputStream().use {
     val bytes = it.readBytes()

use can be invoked on anything that implements the Closeable interface, and when the use block ends (whether normally or due to an exception), close() will be called on the object upon which you invoked use. If an exception is raised within the block or by close(), it will bubble out of use. If both the block and close() raise, it's the exception from the block that will bubble out.

Thus, you can create something resource manager-like by creating a class that implements Closeable, does its setup work in init, and does its cleanup work in close().

In case you're wondering about how use, which is a function, can just be followed by a block like that, see the section on DSL support.

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