string - 预期的struct `std::string::String`，找到的struct `std::str::Split`

我正在制作一个程序，计算用户输入的日期之间的天数之差。到目前为止，我能够使程序使用字符串文字，但不能使用字符串对象。

use std::io;

fn main() {
    let mut date_1 = "22/8/2019".split("/");
    let mut date_2 = "30/8/2019".split("/");
    let vec_1: Vec<&str> = date_1.collect();
    let vec_2: Vec<&str> = date_2.collect();
    println!("{:#?}", vec_1);
    println!("{:#?}", vec_2);
    let my_int_2 = vec_2[0].parse::<i32>().unwrap();
    let my_int_1 = vec_1[0].parse::<i32>().unwrap();
    let result = my_int_2 - my_int_1;
    println!("The difference between two dates is: {}", result);
}

输出:

[
    "22",
    "8",
    "2019",
]
[
    "30",
    "8",
    "2019",
]
The difference between two dates is: 8

我想询问用户的日期:

use std::io;

fn main() {
    let mut date_1 = String::new();
    println!("Enter a date in (dd/mm/yy) format: ");
    io::stdin()
        .read_line(&mut date_1)
        .ok()
        .expect("Couldn't read line");

    let mut date_2 = String::new();
    println!("Enter a date in (dd/mm/yy) format: ");
    io::stdin()
        .read_line(&mut date_2)
        .ok()
        .expect("Couldn't read line");
    date_1 = date_1.split("/");
    date_2 = date_2.split("/");
    let vec_1: Vec<&str> = date_1.collect();
    let vec_2: Vec<&str> = date_2.collect();
    println!("{:#?}", vec_1);
    println!("{:#?}", vec_2);
    let my_int_2 = vec_2[0].parse::<i32>().unwrap();
    let my_int_1 = vec_1[0].parse::<i32>().unwrap();
    let result = my_int_2 - my_int_1;
    println!("The difference between two dates is: {}", result);
}

输出:

   Compiling twentythree v0.1.0 (C:\Users\Muhammad.3992348\Desktop\rust\hackathon\twentythree)
error[E0308]: mismatched types
  --> src\main.rs:15:14
   |
15 |     date_1 = date_1.split("/");
   |              ^^^^^^^^^^^^^^^^^ expected struct `std::string::String`, found struct `std::str::Split`
   |
   = note: expected type `std::string::String`
              found type `std::str::Split<'_, &str>`

error[E0308]: mismatched types
  --> src\main.rs:16:14
   |
16 |     date_2 = date_2.split("/");
   |              ^^^^^^^^^^^^^^^^^ expected struct `std::string::String`, found struct `std::str::Split`
   |
   = note: expected type `std::string::String`
              found type `std::str::Split<'_, &str>`

error[E0599]: no method named `collect` found for type `std::string::String` in the current scope
  --> src\main.rs:19:35
   |
19 |     let vec_1: Vec<&str> = date_1.collect();
   |                                   ^^^^^^^
   |
   = note: the method `collect` exists but the following trait bounds were not satisfied:
           `&mut std::string::String : std::iter::Iterator`
           `&mut str : std::iter::Iterator`

error[E0599]: no method named `collect` found for type `std::string::String` in the current scope
  --> src\main.rs:20:35
   |
20 |     let vec_2: Vec<&str> = date_2.collect();
   |                                   ^^^^^^^
   |
   = note: the method `collect` exists but the following trait bounds were not satisfied:
           `&mut std::string::String : std::iter::Iterator`
           `&mut str : std::iter::Iterator`

error: aborting due to 4 previous errors

Some errors occurred: E0308, E0599.
For more information about an error, try `rustc --explain E0308`.
error: Could not compile `twentythree`.

To learn more, run the command again with --verbose.

如何将字符串对象转换为字符串文字或运行该程序的其他方法。

最佳答案

问题是这样的:

let mut date_1 = String::new(); /* type: std::string::String */
// ...
date_1 = date_1.split("/"); /* type: std::str::Split<'_, &str> */

您已经声明了一种类型(String)的变量，但是您正在尝试为其分配其他类型(std::str::Split)的变量。

解决此问题的一种“Rust-y”方法通常是重新声明一个具有相同名称的变量:

let date_1 = String::new(); /* type: std::string::String */
// ...
let date_1 = date_1.split("/"); /* type: std::str::Split<'_, &str> */

第二个date_1是一个不同的变量(因此它可以具有不同的类型)，但是它与前一个变量具有相同的名称，因此它“阴影化”了前一个变量(这意味着您不能再通过名称来引用它了)。