Rust 不满足 trait bound答案

【问题标题】：The trait bound is not satisfied in RustRust 不满足 trait bound
【发布时间】：2016-08-29 15:50:49
【问题描述】：

我正在尝试用 Rust 编写井字游戏，但是这个更改字段的功能不起作用，我不知道它有什么问题：

fn change_field(mut table: [char; 9], field: i32, player: char) -> bool {
    if field > 0 && field < 10 {
        if table[field - 1] == ' ' {
            table[field - 1] = player;
            return true;
        } else {
            println!("That field isn't empty!");
        }
    } else {
        println!("That field doesn't exist!");
    }

    return false;
}

我收到以下错误：

src/main.rs:16:12: 16:26 error: the trait bound `[char]: std::ops::Index<i32>` is not satisfied [E0277]
src/main.rs:16         if table[field-1] == ' ' {
                          ^~~~~~~~~~~~~~
src/main.rs:16:12: 16:26 help: run `rustc --explain E0277` to see a detailed explanation
src/main.rs:16:12: 16:26 note: slice indices are of type `usize`
src/main.rs:17:13: 17:27 error: the trait bound `[char]: std::ops::Index<i32>` is not satisfied [E0277]
src/main.rs:17             table[field-1] = player;
                           ^~~~~~~~~~~~~~
src/main.rs:17:13: 17:27 help: run `rustc --explain E0277` to see a detailed explanation
src/main.rs:17:13: 17:27 note: slice indices are of type `usize`
src/main.rs:17:13: 17:27 error: the trait bound `[char]: std::ops::IndexMut<i32>` is not satisfied [E0277]
src/main.rs:17             table[field-1] = player;
                           ^~~~~~~~~~~~~~

在更高版本的 Rust 中，我收到以下错误：

error[E0277]: the trait bound `i32: std::slice::SliceIndex<[char]>` is not satisfied
 --> src/main.rs:3:12
  |
3 |         if table[field - 1] == ' ' {
  |            ^^^^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
  |
  = help: the trait `std::slice::SliceIndex<[char]>` is not implemented for `i32`
  = note: required because of the requirements on the impl of `std::ops::Index<i32>` for `[char]`

error[E0277]: the trait bound `i32: std::slice::SliceIndex<[char]>` is not satisfied
 --> src/main.rs:4:13
  |
4 |             table[field - 1] = player;
  |             ^^^^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
  |
  = help: the trait `std::slice::SliceIndex<[char]>` is not implemented for `i32`
  = note: required because of the requirements on the impl of `std::ops::Index<i32>` for `[char]`

这是我在 Rust 中的第一个项目，所以我没有太多经验。我也尝试将字段更改为u32。

【问题讨论】：

标签： rust

【解决方案1】：

原因在备注中告诉你：

note: slice indices are of type `usize`

slice indices are of type `usize` or ranges of `usize`

您需要将i32 值强制转换为usize，例如：

table[(field - 1) as usize]

或者，如果在您的应用程序中有意义，请考虑使用usize 作为field 变量的类型。

【讨论】：