在 Rust 中比较函数的相等性 [英] Comparing functions for equality in Rust

问题描述

我有一个函数，它接受一个数字作为参数，然后根据这个数字返回一个函数.根据许多不同的事情，它可能会返回大约 50 个函数中的任何一个，并且它应该返回的情况变得非常复杂.因此，我想构建一些测试以确保返回正确的函数.到目前为止，我所拥有的大致如下.

I have a function which takes a number as an argument, and then returns a function based on the number. Depending on many different things, it might return any of ~50 functions, and the cases for which one it should return get pretty complicated. As such, I want to build some tests to make sure the proper functions are being returned. What I have so far looks roughly like this.

fn pick_a_function(decider: u32) -> fn(&mut SomeStruct) {
    match decider {
        1 => add,
        2 => sub,
        _ => zero,
    }
}

fn add(x: &mut SomeStruct) {
    x.a += x.b;
}

fn sub(x: &mut SomeStruct) {
    x.a -= x.b;
}

fn zero(_x: &mut SomeStruct) {
    x.a = 0;
}

fn main() {
    let mut x = SomeStruct { a: 2, b: 3 };
    pick_a_function(1)(&mut x);

    println!("2 + 3 = {}", x.a);
}

#[cfg(test)]
mod tests {
    use super::*;

    fn picks_correct_function() {
        assert_eq!(pick_a_function(1), add);
    }
}

问题是这些函数似乎没有实现 Eq 或 PartialEq 特性，所以 assert_eq! 只是说它可以不要比较它们.我有哪些选项可以将返回的函数与正确的函数进行比较?

The problem is that the functions don't seem to implement the Eq or PartialEq traits, so assert_eq! just says that it can't compare them. What options do I have for comparing the returned function to the correct function?

推荐答案

你应该比较结果而不是函数，例如:

You should compare the result instead of the function,for example:

#[cfg(test)]
mod tests {
    use super::*;

    fn picks_correct_function() {
      let add_picked = pick_a_function(1);
      assert_eq!(add_picked(1,2), add(1,2));
    }
}

或者在更复杂的场景中，您可以比较函数的输入，该函数采用一个参数，另一个采用两个参数，尝试调用其中任何一个，看看是否出现编译器错误.

Or in more complex scenarios you can compare the inputs making a function that takes one parameter and another that takes two,try to call any of them and see if you get a compiler error.

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