From/TryFrom 的 Rust 实现应该针对引用还是值? [英] Should Rust implementations of From/TryFrom target references or values?

问题描述

我应该写:

impl<'a> From<&'a Type> for OtherType

或者应该是

impl From<Type> for OtherType

我很难找到答案，可能是因为我的词汇量不足.我真的不是特别关心论点的参考性/价值性.

I'm having a difficult time finding the answer, perhaps due to a vocabulary failure on my part. I really don't particularly care about the reference-ness/value-ness of the argument.

在 C++ 中，我会在值上定义函数 over/method 并在 const 引用上调用它.

In C++, I would define the function over/method on values and calling it on const references.

是否有从impl Trait到impl<'a>的自动推导?特性<&'a Type>?

推荐答案

From/TryFrom 的 Rust 实现应该以引用或值为目标吗?

Should Rust implementations of From/TryFrom target references or values?

是的，他们应该.

这里没有技巧:实现特征以转换您拥有的任何类型.如果你有一个 String，实现它从 Strings 转换.如果您有 &str，请将其实现为从 &str 转换.如果两者都有，请为两者都实施.

There's no trickery here: implement the traits to convert whatever types you have. If you have a String, implement it to convert from Strings. If you have a &str, implement it to convert from &strs. If you have both, implement it for both.

是否有从impl Trait到impl<'a>的自动推导?特性<&'a Type>?

不，并且有充分的理由.例如，考虑这个转换:

No, and for good reason. For example, consider this conversion:

struct Filename(String);

impl From<String> for Filename {
    fn from(value: String) -> Filename {
        Filename(value)
    }
}

编译器没有明显正确的方法来实现对 String 的引用.但是，您可以自己实现它:

There's no obviously correct way for the compiler to implement that for a reference to a String. However, you can implement it yourself:

impl<'a> From<&'a str> for Filename {
    fn from(value: &'a str) -> Filename {
        String::into(value.to_owned())
    }
}

<小时>

如果您不能使用传入的分配，则没有太多理由按值接受参数，因此您不妨接受一个引用.但是，我想说不太将From 用于此类转换——不过也并非闻所未闻.

---

If you can't make use of the incoming allocation, then there's not much reason to accept the argument by value, so you might as well accept a reference. However, I'd say it's less common to use From for such conversions — not unheard of, though.

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