Dynamische Fehlertypen

Sometimes we want to allow any type of error to be returned without writing our own enum covering all the different possibilities. The std::error::Error trait makes it easy to create a trait object that can contain any error.

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Speaker Notes

This slide should take about 5 minutes.

The read_count function can return std::io::Error (from file operations) or std::num::ParseIntError (from String::parse).

Boxing errors saves on code, but gives up the ability to cleanly handle different error cases differently in the program. As such it's generally not a good idea to use Box<dyn Error> in the public API of a library, but it can be a good option in a program where you just want to display the error message somewhere.

Make sure to implement the std::error::Error trait when defining a custom error type so it can be boxed.