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Of all the recipes in this chapter, this one is probably the most stable, as it is being considered for immediate stabilization. The discussion can be found at https://github.com/rust-lang/rust/issues/34511.

While you can use abstract return types for some forms of dependency inversion, you cannot use them for traditional Java-style factories that return different objects depending on a parameter. This is because abstract return types only hide the specific struct returned on the outside of the function, but still internally rely on a specific return value. Because of this, the following code will not compile:

trait Animal {
    fn do_sound(&self);
}

struct Dog;
impl Animal for Dog {
    fn do_sound(&self) {
        println!("Woof");
    }
}
struct Cat;
impl Animal for Cat {
    fn do_sound(&self) {
        println!("Meow");
    }
}

enum AnimalType {
    Dog,
    Cat,
}

fn create_animal(animal_type: AnimalType) -> impl Animal {
    match animal_type...