Languages like haxe simply won't compile if you don't cover every enum value in a switch case. Would that not be preferable? I quite like that feature.
F# I believe is similar wrt discriminated unions and pattern matching
By default Rust expects you to handle every enum variant. Not doing so would be a compile error.
An example - my library exposes enum Colour with 3 variants - Red, Blue Green. In your application code you `match` on all 3. So far so good. But now if I add a 4th colour to my enum, your code will no longer compile because you are no longer handling every enum variant. This is a crappy experience for the user of the library.
Instead, the library writer can make their intent clear - with the #[non_exhaustive] attribute. On such an enum it's not enough to handle the 3 colours of the enum, you must add a wildcard matcher that matches any variants added in future. This gives the library writer flexibility to make changes, while protecting the application developer from breakage.
By default Rust expects you to handle every enum variant. Not doing so would be a compile error.
An example - my library exposes enum Colour with 3 variants - Red, Blue Green. In your application code you `match` on all 3. So far so good. But now if I add a 4th colour to my enum, your code will no longer compile because you are no longer handling every enum variant. This is a crappy experience for the user of the library.
Instead, the library writer can make their intent clear - with the #[non_exhaustive] attribute. On such an enum it's not enough to handle the 3 colours of the enum, you must add a wildcard matcher that matches any variants added in future. This gives the library writer flexibility to make changes, while protecting the application developer from breakage.