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Seals are not just sea mammals
A guide through Kotlin's 'sealed' keyword and what you can do with it.
The more time you spend using Kotlin, the more you are going to realize how magnificent of a language it actually is. I just recently hit a new “peak” of admiration for this language by discovering the
Have a look at the code sample below:
We have a
sealed class Response, representing the response from e.g. a network request and two data classes (
Error) derived from
Response. At first glance, this looks like nothing more than a simple example of inheritance (and some mixed in generics), when in fact it is a very clever way of using actual classes (and the increased possibilities that go along with them) as
Let’s spin this a little bit further:
The magic behind all this is the fact that Kotlin allows you to use
sealed classes as cases for the
when() statement - by doing so, the classes shown above are nothing more than a complex enum with added functionality.
main() function above clearly shows the benefit of being able to create a function like
print(response: Response) without having to worry about the actual type being passed to the function.
The output of the main function obviously looks as follows:
I hope this short post could give you a quick insight into the nature of Kotlin’s
sealed keyword and will help you to write cleaner and easier maintainable code in the future.
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