找不到类型为 `hyper::mime::Mime` 的名为 `from_str` 的函数或关联项 [英] no function or associated item named `from_str` found for type `hyper::mime::Mime`

问题描述

我正在使用 Hyper 0.11，它会重新导出板条箱mime".我正在尝试从字符串创建 MIME 类型:

I'm using Hyper 0.11 which re-exports the crate "mime". I'm trying to create a MIME type from a string:

extern crate hyper;

fn main() {
    let test1 = hyper::mime::Mime::from_str("text/html+xml").unwrap();
}

错误:

error[E0599]: no function or associated item named `from_str` found for type `hyper::<unnamed>::Mime` in the current scope

为什么会出现这个错误，原因是什么?如何解决?

Why is this error, what's the cause? How to fix it?

推荐答案

你得到这个错误是因为，果然，没有在 Mime.为了解析像 Mime::from_str 这样的名称，from_str 必须是 Mime 的固有方法(不是特征的一部分)，或在使用它的地方范围内的特征的一部分.FromStr 不在范围内，因此您会收到错误消息——尽管错误消息甚至会告诉您出了什么问题以及如何解决:

You get this error because, sure enough, there is no from_str method defined on Mime. In order to resolve a name like Mime::from_str, from_str has to be either an inherent method of Mime (not part of a trait), or part of a trait that is in scope in the place where it's used. FromStr isn't in scope, so you get an error -- although the error message goes so far as to tell you what's wrong and how to fix it:

error[E0599]: no function or associated item named `from_str` found for type `hyper::<unnamed>::Mime` in the current scope
 --> src/main.rs:3:13
  |
3 | let test1 = hyper::mime::Mime::from_str("text/html+xml").unwrap();
  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: items from traits can only be used if the trait is in scope
  = note: the following trait is implemented but not in scope, perhaps add a `use` for it:
          candidate #1: `use std::str::FromStr;`

然而，在这种特殊情况下，使用 FromStr 更常见，而不是直接调用 from_str，而是通过 parse str 上的方法，作为 FromStr 的文档 提及.

However, in this particular case, it's more common to use FromStr not by calling from_str directly, but indirectly with the parse method on str, as FromStr's documentation mentions.

let test1: hyper::mime::Mime = "text/html+xml".parse().unwrap();

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