In Dart/Flutter, you can make it explicit when a function can return an error with the Either type from the fpdart package.
For example, parsing a double can throw a FormatException if the input string is not a number, and we can make this part of the function signature. 👇
What's the benefit of this?
You can safely handle both error and success with the fold method, and the type checker will help you to do so.
On the other hand, if you call double.parse directly, you won't get a warning if you forget to handle errors.
Just to be clear: Dart already has a built-in exception handling system.
And throwing exceptions works great when you want them to propagate through the call stack.
Other times, returning an error is preferable to throwing an exception.
So choose accordingly.
Also note that Either is very similar to the Result type that I've covered in tip 62.
The advantage of Either (and fpdart in general) is that it has a more extensive (and well documented) API that works particularly well when dealing with async code.
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