[英]While let chain causing rust-analyzer to complain about the feature being unstable in Rust 1.66, wasn't this just merged into stable recently?
while let Some(peek_ch) = chars.peek() && peek_ch.is_whitespace() {
chars.next();
}
The above code is causing rust to complain with上面的代码导致 rust 抱怨
`let` expressions in this position are unstable
see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
My understanding was if-let and while-let chaining was stabilized?我的理解是 if-let 和 while-let 链接是否稳定? Also, from this error and github issue I can't determine what unstable feature to enable to allow this, how do you normally determine that?
此外,从这个错误和 github 问题我无法确定要启用什么不稳定的功能来允许这个,你通常如何确定?
The problem is that you're not allowed to use &&
with while let
yet because unfortunately the merge of the stabilization had to be reverted问题是你还不允许在
while let
中使用&&
因为不幸的是必须恢复稳定的合并
If you use a nightly compiler it will tell you what feature you have to enable to make it work:如果您使用夜间编译器,它会告诉您必须启用哪些功能才能使其工作:
> cargo +nightly run
...
error[E0658]: `let` expressions in this position are unstable
--> src/main.rs:4:11
|
4 | while let Some(peek_ch) = chars.peek() && peek_ch.is_whitespace() {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
= help: add `#![feature(let_chains)]` to the crate attributes to enable
So this works with nightly rust:所以这适用于夜间 rust:
#![feature(let_chains)]
fn main() {
let mut chars = "hello".chars().peekable();
while let Some(peek_ch) = chars.peek() && peek_ch.is_whitespace() {
chars.next();
}
}
Or you can work around it with one of PeterHalls stable solutions.或者您可以使用 PeterHall 的稳定解决方案之一解决它。
The problem is the &&
, not the while let
.问题是
&&
,而不是while let
。 As written, you are trying to match the result of the expression chars.peek() && peek_ch.is_whitespace()
, but this doesn't make sense because peek
returns an Option<T>
while is_whitespace
returns a bool
.如所写,您正在尝试匹配表达式
chars.peek() && peek_ch.is_whitespace()
的结果,但这没有意义,因为peek
返回Option<T>
而is_whitespace
返回bool
。
The error message is a little bit misleading because it thinks you are trying to use if let
chains , an unstable feature which allows you to match on multiple patterns.该错误消息有点误导,因为它认为您正在尝试使用
if let
chains ,这是一种不稳定的功能,可让您匹配多种模式。
You can rewrite this with:你可以重写这个:
while let Some(peek_ch) = chars.peek() {
if peek_ch.is_whitespace() {
chars.next();
} else {
break;
}
}
Or要么
while let Some(peek_ch) = chars.peek().filter(|c| c.is_whitespace()) {
chars.next();
}
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