Derive Macro IntoVariant

#[derive(IntoVariant)]
{
    // Attributes available to this derive:
    #[enumcapsulate]
}

Derive macro generating an impl of the trait IntoVariant<T>.

It generates an impl for each of the enum’s newtype variants, where Inner is the variant’s field type and Outer is the enclosing enum’s type.

struct Inner;

enum Outer {
    Inner(Inner),
    // ...
}

// The generated impls look something along these lines:

impl IntoVariant<Inner> for Outer {
    fn into_variant(self) -> Result<T, Self> {
        match self {
            Outer::Inner(inner) => Ok(inner),
            err => Err(err),
        }
    }
}

// ...

Note: Despite the derive macro’s name it’s actually TryFrom<T> that’s being derives, not TryInto<T>. But since the macro is derived on the enum the latter feels more appropriate as the derive’s name.