What #[derive(IsVariant)] generates

• 1 Example usage
• 2 What is generated?

When an enum is decorated with #[derive(IsVariant)], for each variant foo in the enum, a public instance method is_foo(&self) -> bool is generated. If you don’t want the is_foo method generated for a variant you can put the #[is_variant(ignore)] attribute on that variant.

1 Example usage

#[derive(IsVariant)]
enum Maybe<T> {
    Just(T),
    Nothing
}

fn main(){
  assert!(Maybe::<()>::Nothing.is_nothing());
  assert!(!Maybe::<()>::Nothing.is_just());
}

2 What is generated?

The derive in the above example code generates the following code:

impl <T> Maybe<T>{
    pub fn is_just(&self) -> bool {
        match self {Self::Just(..) => true, _ => false}
    }
    pub fn is_nothing(&self) -> bool {
        match self {Self::Nothing => true, _ => false}
    }
}