相关疑难解决方法(0)

我可以在Rust中传递函数作为参数(可能是的),如果可以的话,我可以这么做.

如果你不能,这是一个很好的选择.

我尝试了一些语法,但我没有得到

我知道我能做到这一点

fn example() {
    let fun: fn(value: i32) -> i32;
    fun = fun_test;
    fun(5i32);
}

fn fun_test(value: i32) -> i32 {
    println!("{}", value);
    value
}

但不是将函数作为参数传递给另一个函数

fn fun_test(value: i32, (some_function_prototype)) -> i32 {
    println!("{}", value);
    value
}

考虑以下玩具示例:

use std::cmp::Ordering;

pub trait SimpleOrder {
    fn key(&self) -> u32;
}

impl PartialOrd for dyn SimpleOrder {
    fn partial_cmp(&self, other: &dyn SimpleOrder) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for dyn SimpleOrder {
    fn cmp(&self, other: &dyn SimpleOrder) -> Ordering {
        self.key().cmp(&other.key())
    }
}

impl PartialEq for dyn SimpleOrder {
    fn eq(&self, other: &dyn SimpleOrder) -> bool {
        self.key() == other.key()
    }
}

impl Eq for SimpleOrder {}

这不编译.它声称在实施过程中存在一个终身问题partial_cmp:

error[E0495]: cannot infer an appropriate lifetime due …

在github上交叉发布

鉴于以下代码段：

use futures::stream::{self, StreamExt};

async fn from_bar(bar: &[Vec<&u8>]) {
    let x = bar.iter().flat_map(|i| i.iter().map(|_| async { 42 }));
    let foo: Vec<_> = stream::iter(x).collect().await;
}

#[tokio::main]
async fn main() {
    for bar in vec![] {
        tokio::spawn(async {
            from_bar(bar).await;
        });
    }
}

我收到以下错误：

error[E0308]: mismatched types
  --> src/main.rs:11:9
   |
11 |         tokio::spawn(async {
   |         ^^^^^^^^^^^^ one type is more general than the other
   |
   = note: expected type `std::ops::FnOnce<(&&u8,)>`
              found type `std::ops::FnOnce<(&&u8,)>`

error: implementation of `std::iter::Iterator` is not general …