extern crate take_mut;

struct Dog {
    s: String,
}
struct Cat {
    s: String,
}
enum Content {
    SomethingA(Dog),
    SomethingB(Cat),
}

struct A {
    content: Content,
}

fn change(_dog: Dog) -> Cat {
    Cat {
        s: "lucy".to_string(),
    }
}

fn does_not_work(it: &mut A) {
    take_mut::take(&mut it.content, |content| {
        match content {
            Content::SomethingA(dog) => Content::SomethingB(change(dog)),
            Content::SomethingB(cat) => Content::SomethingB(cat),
        }
    });
}

fn main() {
    let mut it = A {
        content: Content::SomethingA(Dog {
            s: "wuff".to_string(),
        }),
    };

    does_not_work(&mut it);

    works();
    works2(&mut it);
}

fn works() {
    let mut a = A {
        content: Content::SomethingA(Dog {
            s: "wuff".to_string(),
        }),
    };

    match a.content {
        Content::SomethingA(dog) => {
            a.content = Content::SomethingB(change(dog));
        }
        Content::SomethingB(cat) => {
            a.content = Content::SomethingB(cat);
        }
    }
}

fn works2(it: &mut A) {
    it.content = Content::SomethingA(Dog {
        s: "wuff".to_string(),
    });
}