我正在学习如何在 Rust 中使用 const 泛型。像这样的简单演示：Playground

有人能告诉我如何使用 const 泛型数组作为返回类型吗？

fn foo<const C: usize>(n: u32) -> [i32; C] {
    // failed
    // [1; 3]
    // failed
    [1; n]
}

fn hoo<const N: usize>(arr: [i32; N]) {
    println!("the array is {:?}", arr);
}

fn main() {
    // Give a number, create a array, this fails
    let f = foo(3);

    // const array as input
    hoo([1]);
    hoo([1, 2, 3]);
}

编译信息如下：

  Compiling playground v0.0.1 (/playground)
error[E0435]: attempt to use a non-constant value in a constant
 --> src/main.rs:2:9
  |
1 | fn foo<const C: usize>(n: u32) -> [i32; C] {
  |                        - this would need to be a `const`
2 |     [1; n]
  |         ^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0435`.
error: could not compile `playground`

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

回答

fn foo<const C: usize>() -> [i32; C] {
    [1; C]
}

foo::<3>();