rust - 请教封装返回泛型数据的问题？

Question

我尝试对redis进行一个简单的封装，遇到返回泛型数据的问题。代码如果下，我希望获取数据时能用泛型指定数据类型：

pub trait Cache {
    async fn get<T>(&self, key: &str) -> Result<T, Error>;
}

实现方法如下：

impl Cache for Redis {
    async fn get<T>(&self, key: &str)-> Result<T, Error> {
        let r = self.conn.get(key).await?;
        Ok(r)
    }
}

提示如下错误：

error[E0277]: the trait bound `T: FromRedisValue` is not satisfied
    --> src/redis.rs:55:21
     |
55   |         let r = self.conn.get(key).await?;
     |                           ^^^ the trait `FromRedisValue` is not implemented for `T`
     |

请问如果不改 T 为 T: FromRedisValue的话，有什么其他解决办法吗？谢谢

Answer 1

use redis::{AsyncCommands, RedisError};

pub trait Cache {
    type Output;

    async fn get<T>(&self, key: &str) -> Result<Self::Output, RedisError>;
}

impl Cache for redis::Client {
    type Output = String;

    async fn get<T>(&self, key: &str) -> Result<Self::Output, RedisError> {
        let mut conn = self.get_async_connection().await?;
        let r: Self::Output = conn.get(key).await?;
        Ok(r)
    }
}