Rust 为什么我不能从带有字符串的 struct 的引用迭代器中收集VEC<；&；str&>

我目前正在学习Ruust，我想从拥有字符串的项目向量中收集字符串的引用(&amp；STR).

struct Channel {
    cid: usize,
    name: String,
}

fn main() {
    let channels: Vec<Channel> = vec![Channel {
        cid: 1,
        name: "Hello".to_string(),
    }];
    let names: Vec<&str> = channels.iter().map(|x| &x.name).collect();
}

此代码无法编译，出现以下错误:

[E0277]: a value of type `Vec<&str>` cannot be built from an iterator over elements of type `&String`
    --> src/main.rs:11:61
     |
11   |     let names: Vec<&str> = channels.iter().map(|x| &x.name).collect();
     |                                                             ^^^^^^^ value of type `Vec<&str>` cannot be built from `std::iter::Iterator<Item=&String>`
     |
     = help: the trait `FromIterator<&String>` is not implemented for `Vec<&str>`
     = help: the trait `FromIterator<&str>` is implemented for `Vec<&str>`
     = help: for that trait implementation, expected `str`, found `String`
note: the method call chain might not have had the expected associated types
    --> src/main.rs:11:44
     |
7    |       let channels: Vec<Channel> = vec![Channel {
     |  __________________________________-
8    | |         cid: 1,
9    | |         name: "Hello".to_string(),
10   | |     }];
     | |______- this expression has type `Vec<Channel>`
11   |       let names: Vec<&str> = channels.iter().map(|x| &x.name).collect();
     |                                       ------ ^^^^^^^^^^^^^^^^ `Iterator::Item` changed to `&String` here
     |                                       |
     |                                       `Iterator::Item` is `&Channel` here
note: required by a bound in `collect`
    --> /playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:2050:19
     |
2050 |     fn collect<B: FromIterator<Self::Item>>(self) -> B
     |                   ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Iterator::collect`

我can通过调用as_str()来提取字符串片来使其工作:

let names: Vec<&str> = channels.iter().map(|x| x.name.as_str()).collect();个

然而，我想了解why这是必需的.根据我的理解，由于德雷夫的胁迫，&String可以转化为&str.为什么我必须明确使用as_str()？此外，在性能方面，取as_str()是否等同于引用一个项？