How to map a parametrized enum from a generic type to another?

Question

If I have a type like MyEnum, how can I map it in cases where not every variant is parameterized?

For example, I\'d like to convert from

Answer 1

I'd create a map method on your enum:

#[derive(Debug)]
enum MyEnum {
    B,
    C,
    D(T),
}

impl MyEnum {
    fn map(self, f: impl FnOnce(T) -> U) -> MyEnum {
        use MyEnum::*;

        match self {
            B => B,
            C => C,
            D(x) => D(f(x)),
        }
    }
}

fn main() {
    let answer = MyEnum::D(42);
    let answer2 = answer.map(|x| x.to_string());
    println!("{:?}", answer2);
}

This is similar to existing map methods, such as Option::map.