rust - 为什么即使我已经实现了 Trait<&str>，特征绑定(bind) Trait<&String> 仍然不满足？

Question

我写了下面的代码:

pub struct Serializer;

pub trait Serialize<T> {
    fn to_bert(&self, data: T) -> Vec<u8>;
}

pub trait Convert<T> {
    fn to_binary(&self, data: T) -> Vec<u8>;
}

impl<'a> Convert<&'a str> for Serializer {
    fn to_binary(&self, data: &'a str) -> Vec<u8> {
        let binary_string = data.as_bytes();
        let binary_length = binary_string.len() as i16;
        let mut binary = vec![];
        binary.write_i16::<BigEndian>(binary_length).unwrap();
        binary.extend(binary_string.iter().clone());
        binary
    }
}

impl Serialize<String> for Serializer {
    fn to_bert(&self, data: String) -> Vec<u8> {
        let binary_string = self.to_binary(&data);
        self.generate_term(BertTag::String, binary_string)
    }
}

impl<'a> Serialize<&'a str> for Serializer {
    fn to_bert(&self, data: &'a str) -> Vec<u8> {
        let binary_string = self.to_binary(data);
        self.generate_term(BertTag::String, binary_string)
    }
}

编译时，我收到一条错误消息，提示编译器找不到正确的调用函数:

error: the trait bound `serializers::Serializer: serializers::Convert<&std::string::String>` is not satisfied [E0277]
let binary_string = self.to_binary(&data);
                         ^~~~~~~~~
help: run `rustc --explain E0277` to see a detailed explanation
help: the following implementations were found:
help:   <serializers::Serializer as serializers::Convert<&'a str>>
help:   <serializers::Serializer as serializers::Convert<types::BertType>>

为什么我给&str指定了生命周期，编译器还是找不到正确的实现？我该如何解决这个问题？

Answer 1

How can I fix this?

通过获取 &str来自 data :

let binary_string = self.to_binary(&*data);

如错误所说，Convert<&String>未针对 Serializer 实现，但是Convert<&str>是。 &data是 &String , 但你需要一个 &str , 写作 &*data产生 &str .

---

请注意，通常(当字符串未更改时)没有必要为 String 实现相同的功能。和 &str , 只有 &str版本应该够了。在您的示例中，您可以删除 Serialize<String> Serializer 的实现并使用 Serialize<&str>相反。

fn main() {
    let mut s = Serializer;
    let a: String = "a".to_string();
    // autoderef &String to &str and call Serialize<&str>::to_bert()
    // I don't know why the autoderef does not work in your original example
    s.to_bert(&a);
}