获取错误“特征 `std::ops::FnMut<(char,)>` 未为 `std::string::String` 实现"；对于简单的类型不匹配 [英] Getting error &quot;the trait `std::ops::FnMut&lt;(char,)&gt;` is not implemented for `std::string::String`&quot; for a simple type mismatch

问题描述

 let mystring = format!("the quick brown {}", "fox...");断言！(mystring.ends_with(mystring));

错误:

特性 `std::ops::FnMut<(char,)>` 没有为 `std::string::String` 实现

将 mystring.ends_with(mystring) 更改为 mystring.ends_with(mystring.as_str()) 修复了它.

为什么这个错误如此神秘?

如果我在不使用格式的情况下创建字符串，请说:

let mystring = String::from_str("The quick brown fox...");断言！(mystring.ends_with(mystring));

错误更容易理解:

error[E0599]: 没有找到类型名为 `ends_with` 的方法`std::result::Result<std::string::String, std::string::ParseError>`在当前范围内

解决方案

这个错误还有很多:

<代码>|断言！(mystring.ends_with(mystring));|^^^^^^^^^ `std::ops::FnMut<(char,)>` 没有为 `std::string::String` 实现|= 注意:因为对`std::string::String` 的`std::str::pattern::Pattern<'_>` impl 的要求是必需的

批判性

<块引用>

注意:因为std::string::String的std::str::pattern::Pattern<'_>的impl的要求，所以需要

String 的.ends_with 接受任何实现了 Pattern 特征的值作为它的搜索模式，而 String 没有实现那个特征.>

如果您查看 Pattern<的文档/code>，它包括

impl<'a, 'b>模式<'a>for &'b 字符串

所以如果您更改，您的代码段就可以正常工作

assert!(mystring.ends_with(mystring));

到

assert!(mystring.ends_with(&mystring));

这也是有道理的，因为否则你会试图将 mystring 的所有权传递给 ends_with 函数，这似乎不是没错.

至于你看到的具体错误，Pattern 的 trait 定义也包括

impl<'a, F>模式<'a>对于 F在哪里F: FnMut(char) ->布尔，

通常表示函数接受一个字符并返回一个布尔计数作为模式，导致消息说 String 与该特征实现不匹配.

    let mystring = format!("the quick brown {}", "fox...");
    assert!(mystring.ends_with(mystring));

Error:

the trait `std::ops::FnMut<(char,)>` is not implemented for `std::string::String`

Changing mystring.ends_with(mystring) to mystring.ends_with(mystring.as_str()) fixes it.

Why is this error so cryptic?

If I create the string without using format, say:

let mystring = String::from_str("The quick brown fox...");
assert!(mystring.ends_with(mystring));

The error is much more understandable:

error[E0599]: no method named `ends_with` found for type
`std::result::Result<std::string::String, std::string::ParseError>`
in the current scope

解决方案

There's more to that error:

| assert!(mystring.ends_with(mystring));
|                  ^^^^^^^^^ the trait `std::ops::FnMut<(char,)>` is not implemented for `std::string::String`
|
= note: required because of the requirements on the impl of `std::str::pattern::Pattern<'_>` for `std::string::String`

critically

note: required because of the requirements on the impl of std::str::pattern::Pattern<'_> for std::string::String

String's .ends_with accepts any value that implements the Pattern trait as its search pattern, and String does not implement that trait.

If you look at the documentation for Pattern, it includes

impl<'a, 'b> Pattern<'a> for &'b String

so your snippet works fine if you change

assert!(mystring.ends_with(mystring));

to

assert!(mystring.ends_with(&mystring));

It also makes sense because otherwise you'd be trying to pass ownership of mystring to the ends_with function, which doesn't seem right.

As for the specific error you were seeing, Pattern's trait definition also includes

impl<'a, F> Pattern<'a> for F 
where
    F: FnMut(char) -> bool, 

which generically says functions accepting a char and returning a boolean count as patterns, leading to the message saying String does not match that trait implementation.

这篇关于获取错误“特征 `std::ops::FnMut<(char,)>` 未为 `std::string::String` 实现"；对于简单的类型不匹配的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！