如何将函数指针存储在数组中? [英] How can I store function pointers in an array?

问题描述

如何将函数(或函数指针)粘贴到数组中以进行测试?

How do you stick functions (or function pointers) into an array for testing purposes?

fn foo() -> isize { 1 }
fn bar() -> isize { 2 }

fn main() {
    let functions = vec![foo, bar];
    println!("foo() = {}, bar() = {}", functions[0](), functions[1]());
}

Rust playground

这是我得到的错误代码:

This is the error code I get:

error: mismatched types:
 expected `fn() -> isize {foo}`,
    found `fn() -> isize {bar}`
(expected fn item,
    found a different fn item) [E0308]

    let functions = vec![foo, bar];
                              ^~~

尽管具有相同的签名，但 Rust 将我的函数(值)视为不同的类型，这让我感到惊讶.

Rust is treating my functions (values) as different types despite having the same signatures, which I find surprising.

推荐答案

在最近的某个时候，每个函数都有自己独特的类型，原因……我不记得了.结果是你需要给编译器一个提示(注意 functions 上的类型):

At some point recently, each function was given its own, distinct type for... reasons that I don't recall. Upshot is that you need to give the compiler a hint (note the type on functions):

fn foo() -> isize {
    1
}
fn bar() -> isize {
    2
}
fn main() {
    let functions: Vec<fn() -> isize> = vec![foo, bar];
    println!("foo() = {}, bar() = {}", functions[0](), functions[1]());
}

你也可以这样做:

let functions = vec![foo as fn() -> isize, bar];

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