在 Rust 中通过关联类型实现一个 trait 的问题

Question

我有这个特点：

trait Pokemon {
    type Move;
    fn pick_move(&self) -> Self::Move;
}

某些类型实现了 trait，如下所示：

#[derive(PartialEq, Clone, Copy)]
enum Fire {
    Charmander,
    Charmeleon,
    Charizard
}

#[derive(PartialEq, Clone, Copy)]
enum FireMove {
    Ember, FlameThrower, FireBlast
}

#[derive(PartialEq, Clone, Copy)]
enum Water {
    Squirtle,
    Wartortle,
    Blastoise
}

#[derive(PartialEq, Clone, Copy)]
enum WaterMove {
    Bubble,
    WaterGun
}

impl Pokemon for Fire {
    type Move = FireMove;

    fn pick_move(&self) -> Self::Move {
        match self {
            Self::Charmander => Self::Move::Ember,
            Self::Charmeleon => Self::Move::FlameThrower,
            Self::Charizard => Self::Move::FireBlast,
        }
    }
}

impl Pokemon for Water {
    type Move = WaterMove;

    fn pick_move(&self) -> Self::Move {
        if *self == Water::Squirtle {
            return Self::Move::Bubble;
        }
        Self::Move::WaterGun
    }
}

对于实现Pokemon trait 的类型，我想实现一个 trait Battle ：

trait Battle {
  fn battle(&self) -> ??;
}

最后，我想要实现的是我应该能够在任何实现Pokemon特性的类型上调用.battle并最终能够返回赢得战斗的 Pokemon。

我也考虑过使用这样的方法：

fn battle<T>(pokemon: T, foe: T) -> T
where T: Pokemon
{
    let p_move = pokemon.pick_move();
    let f_move = foe.pick_move();

    if p_move == f_move {
        return pokemon;
    }

    foe
}

不幸的是，在这里我无法比较已传递参数的Move 。

我接近实现这一目标的一种方法是做这样的事情：

trait Battle {
    type Pokemons;
    
    fn battle(&self, foe: Self::Pokemons) -> Self::Pokemons;
}

#[derive(PartialEq, Clone, Copy)]
enum PokemonTypes {
    Fire(Fire),
    Water(Water),
    Grass(Grass)
}

impl Battle for Fire {
    type Pokemons = PokemonTypes;

    fn battle(&self, foe: Self::Pokemons) -> Self::Pokemons {
        match foe {
            Self::Pokemons::Water(pokemon) => Self::Pokemons::Water(pokemon),
            _ => Self::Pokemons::Fire(*self) // because Fire beats Grass type
        }
    }
}

所以基本上，我如何实现这个Battle特性来帮助我比较动作和/或口袋妖怪类型并决定获胜者？

Answer 1

您可以将移动类型抽象为另一个枚举，并删除特征中的关联类型：

#[derive(PartialEq, Clone, Copy)]
enum Move {
    Water(WaterMove),
    Fire(FireMove),
}

trait Pokemon {
    fn pick_move(&self) -> Move;
}

然后以同样的方式，您可以直接使用Battle系统的实现，但通过PokemonType实现对战：

#[derive(PartialEq, Clone, Copy)]
enum PokemonType {
    Fire(Fire),
    Water(Water),
}

trait Battle {
    fn battle(&self, foe: PokemonType) -> PokemonType;
}

impl Battle for PokemonType {
    fn battle(&self, foe: PokemonType) -> PokemonType {
        match (self, foe) {
            (p1@PokemonType::Water(_), p2@PokemonType::Fire(_)) => {
                *p1
                // do watever
            }
            _ => foe // handle other patterns
        }
    }
}

操场