rust - 如何返回一个常量值？

Question

我想写一个小的阶乘库。请查看库主模块中的代码:

pub fn results() -> const [i8; 6] { [
      1,
      1,
      2,
      6,
     24,
    120,
    //720 is too large for i8.
] }

pub fn results() -> const [i32; 13] { [
              1,
              1,
              2,
              6,
             24,
            120,
            720,
          5_040,
         40_320,
        362_880,
      3_628_800,
     39_916_800,
    479_001_600,
    //6_227_020_800 is too large for i32.
] }

对于第一个函数的返回类型，它给我这个错误:

error: expected type, found keyword `const`
 --> src/main.rs:1:21
  |
1 | pub fn results() -> const [i8; 6] { [
  |                     ^^^^^

目标是在编译时获取所有可能阶乘值的数组。

Answer 1

get an array of all possible factorial values at compile time

只需声明常量值:

pub const RESULTS_I8: [i8; 6] = [1, 1, 2, 6, 24, 120];

pub const RESULTS_I32: [i32; 13] = [
    1,
    1,
    2,
    6,
    24,
    120,
    720,
    5_040,
    40_320,
    362_880,
    3_628_800,
    39_916_800,
    479_001_600,
];

根本没有理由涉及一个函数，因为不需要计算!