rust - 防 rust 测试不断出现错误。我需要包括一些测试内容吗？

Question

我的代码本身可以在文件中工作，但是每当我尝试运行RuSTLings quiz1.rs时，代码的测试部分都会出错。

// GOAL OF PROGRAM
// Mary is buying apples. One apple usually costs 2 Rustbucks, but if you buy
// more than 40 at once, each apple only costs 1! Write a function that calculates
// the price of an order of apples given the order amount. No hints this time

fn calculate_apple_price(apples: i32){
    let mut price = 2;
    if apples >= 40 {
        price = 1;
    }
}

// Don't modify this function!
#[test]
fn verify_test() {
    let price1 = calculate_apple_price(35); 
    let price2 = calculate_apple_price(65); 

    assert_eq!(70, price1); // Error happens here 'no implementation for `{integer} == ()`'
    assert_eq!(65, price2);// Error happens here 'no implementation for `{integer} == ()`'
} 

我用谷歌搜索了问题并尝试了rust的解释，但是我对Rust还是陌生的。有人可以用简单的英语解释这个错误吗？

Answer 1

您忘记为fn calculate_apple_price指定返回类型，price1和price2填充了零大小的类型(这在您学习RUST时可能会造成混淆)。
你应该尝试这样的事情

fn calculate_apple_price(apples: i32) -> i32 /* specify i32 as return type */ {
    let mut price = 2;
    if apples >= 40 {
        price = 1;
    }
    price // Return the price (the `return` keyword is optional in this case)
}