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问题[rust]

Martin Hope
Dima
Asked: 2025-03-24 20:11:46 +0000 UTC
  • 5

这可能是一个愚蠢的错误，但我不明白这意味着什么。我请求帮助。为什么不应用条件运算符内部获得的新值（let oldfiles:u64 = 6666;），而是使用旧值（let oldfiles:u64 = 5555;）？条件if true已满足。

   let oldfiles:u64 = 5555;  
          
   if true {
       let oldfiles:u64 = 6666;
       dbg!(oldfiles); // oldfiles = 6666
   }

   //почему здесь значение oldfiles не изменилось и равно 5555 ?
   dbg!(oldfiles); // oldfiles = 5555
rust
Martin Hope
Alex
Asked: 2025-03-22 18:01:24 +0000 UTC
  • 7

对第一个向量进行排序后，如何正确组织 四个逻辑上相互连接的向量之间的数据同步？ 例如，我最初有：


let mut v01: Vec<&str> = vec!["111", "abc", "ghi", "222"];
let mut v02: Vec<&str> = vec!["One", "A", "G", "Two"];
let mut v03: Vec<&str> = vec!["i32", "&str", "&str", "i64"];
let mut v04: Vec<&str> = vec!["true", "false", "false", "true"];

之后let _ = v01.sort();
           ...
我想要得到这个结果：

["111", "abc", "ghi", "222"]
...
результат:

["111", "222", "abc", "ghi"]
["One", "Two", "A", "G"]
["i32", "i64", "&str", "&str"]
["true", "true", "false", "false"]

有两种情况很有趣：
（1）当向量 v01 没有重复元素时；
（2）当 v01 具有重复元素时，例如，v04对于此类（重复）元素具有不同的值。

rust
Martin Hope
Alex
Asked: 2025-03-20 04:38:22 +0000 UTC
  • 5

如何修复代码行：if v.iter().any(|i| *i == s) {
匹配时获取向量索引，例如： Yes -> 1。

fn main() {

 let v: Vec<&str> = vec!["abc", "des", "xyz", "qwe"];   
    
 for (ind, val) in v.iter().enumerate() {
    
    println!("{} - {}", ind, val);
 }

 let s: &str = "des";    

 if v.iter().any(|i| *i == s) {
    println!("Yes");
    // println!("Yes -> {:?}", index_of_v); // Yes -> 1
    } else {
    println!("No");
 }    
}
rust
Martin Hope
Dima
Asked: 2025-02-25 16:27:14 +0000 UTC
  • 5

告诉我错误是什么或者从哪里寻找原因？为什么在这种情况下我们会得到不同的类型？

   let client = Client::connect("postgresql://user:pass@localhost:5432/base", NoTls).unwrap(); 

    match client {
        Ok(mut client) => {
            let stmt = client.prepare("INSERT INTO status (status) VALUES ($1)").unwrap();
      
            client
                .execute(&stmt, &[&json_data])
                .expect("Failed to execute statement");
      
            println!("JSON data inserted successfully");
        }
        Err(err) => println!("Error: {}", err),
    }

给出消息：

error[E0308]: mismatched types
   --> src/main.rs:252:9
    |
251 |     match client {
    |           ------ this expression has type `postgres::Client`
252 |         Ok(mut client) => {
    |         ^^^^^^^^^^^^^^ expected `Client`, found `Result<_, _>`
    |
    = note: expected struct `postgres::Client`
                 found enum `Result<_, _>`
rust
Martin Hope
Alex
Asked: 2025-02-09 18:22:44 +0000 UTC
  • 5

如何修正代码以避免错误：
'a', 'b' -- is borrowed here
returns a value referencing data owned by the current function？

use std::collections::HashMap;

#[derive(Debug)]
struct Error;

fn f1(s: &str) -> Result<&str, Error> { 
   // something for test:
   if s.len() > 5 {
      Ok(s)
   }else{
      Err(Error)
   }      
}

fn f2(s: &str) -> Result<&str, Error> { 
   todo!() 
}



fn r(raw: HashMap<String, String>) -> Result<HashMap<&'static str, &'static str>, Error> {
    raw
        .into_iter()
        .map(|(a, b)| {
            
            // println!("{:?} - {:?}", a, b);
            Ok((
                f1(&a)?,
                f2(&b)?,
            ))
        })
        .collect()
}



fn main() {
    let raw: HashMap<String, String> = HashMap::from([
       ("Mercury".to_string(), "0.4".to_string()),
       ("Venus".to_string(), "0.7".to_string()),
       ("Earth".to_string(), "1.0".to_string()),
       ("Mars".to_string(), "1.5".to_string()),
    ]);
    
    println!("{:?}", r(raw));
}
rust