rust - 如何在 Rust 中制作调度表？-6ren

rust - 如何在 Rust 中制作调度表？

转载作者：行者123 更新时间：2023-11-29 08:23:27

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我正在尝试构建一个简单的 RPN 计算器，并且我已经掌握了基础知识。我想做一个 dispatch table实现各种计算器功能。如果我在 Perl 中这样做，我会这样写:

my %ops = (
  '+' => sub { +shift + +shift; },
  '-' => sub { +shift - +shift; },
  '*' => sub { +shift * +shift; },
  '/' => sub { +shift / +shift; }
);

或者在 JavaScript 中:

let ops = {
    "+": (a, b) => a + b,
    "-": (a, b) => a - b,
    "*": (a, b) => a * b,
    "/": (a, b) => a / b
};

这是我迄今为止在 Rust 中尝试过的:

use std::collections::HashMap;

fn main() {
    println!("Going to call +");

    let dispatch = HashMap::new();

    dispatch.insert(String::from("+"), |a, b| a + b);
    dispatch.insert(String::from("-"), |a, b| a - b);

    let plus = dispatch.get(&String::from("+"));
    println!("2 + 3 = {}", plus(2, 3));

    let minus = dispatch.get(&String::from("-"));
    println!("2 - 3 = {}", minus(2, 3));
}

当我尝试编译时，出现以下错误:

error[E0308]: mismatched types
 --> src/main.rs:9:40
  |
9 |     dispatch.insert(String::from("-"), |a, b| a - b);
  |                                        ^^^^^^^^^^^^ expected closure, found a different closure
  |
  = note: expected type `[closure@src/main.rs:8:40: 8:52]`
             found type `[closure@src/main.rs:9:40: 9:52]`
  = note: no two closures, even if identical, have the same type
  = help: consider boxing your closure and/or using it as a trait object

error[E0618]: expected function, found enum variant `plus`
  --> src/main.rs:12:28
   |
11 |     let plus = dispatch.get(&String::from("+"));
   |         ---- `plus` defined here
12 |     println!("2 + 3 = {}", plus(2, 3));
   |                            ^^^^^^^^^^ not a function
help: `plus` is a unit variant, you need to write it without the parenthesis
   |
12 |     println!("2 + 3 = {}", plus);
   |                            ^^^^

error[E0618]: expected function, found enum variant `minus`
  --> src/main.rs:15:28
   |
14 |     let minus = dispatch.get(&String::from("-"));
   |         ----- `minus` defined here
15 |     println!("2 - 3 = {}", minus(2, 3));
   |                            ^^^^^^^^^^^ not a function
help: `minus` is a unit variant, you need to write it without the parenthesis
   |
15 |     println!("2 - 3 = {}", minus);
   |                            ^^^^^