我们什么时候应该在 Rust 中使用 unwrap 和 expect [英] When should we use unwrap vs expect in Rust

问题描述

我是 Rust 的新手，并试图了解我们什么时候应该使用 unwrap 和 expect.

I'm new to rust and trying to understand when should we use unwrap vs expect.

这是一个示例代码:

use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();

    let query = args.get(1).unwrap();
    println!("query from unwrawp: {}", query);

    let query = args.get(1).expect("insufficient arguments");
    println!("query from expect: {}", query);

    //$ cargo run hello
    //OUTPUT:
    //query from expect: hello
    //query from unwrawp: hello

}

我观察到的唯一区别是期望中有一个自定义的恐慌消息.
这两个是可以互换的，还是有什么特殊的场景我们应该使用一个而不是另一个?

Only difference I observed is there's a custom panic message in expect.
Are these two interchangeable or are there any special scenarios where we should use one over the other?

推荐答案

Rust 没有函数重载，所以应该有一种方法来声明unwrap with a message"，那就是expect.

Rust doesn't have function overloading, so there should be a way to declare "unwrap with a message", and that is expect.

1. expect == unwrap 带有消息
2. expect_err == unwrap_err 带有消息

1. expect == unwrap with a message
2. expect_err == unwrap_err with a message

关于unwrap vs expect"的使用场景Rust Book(第 9 章) 说:

About usage scenarios of "unwrap vs expect" Rust Book (Ch 9) says:

使用 expect 而不是 unwrap 并提供良好的错误消息可以传达您的意图并更容易追踪恐慌的来源.因为此错误消息以我们指定的文本开头...更容易找到此错误消息来自代码的何处.

Using expect instead of unwrap and providing good error messages can convey your intent and make tracking down the source of a panic easier. Because this error message starts with the text we specified... it will be easier to find where in the code this error message is coming from.

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