result and ?

Result<T> 是一个枚举类型用于描述返回的结果或错误，它包含两个成员(变体 variants) :

• Ok(T): 返回一个结果值 T
• Err(e): 返回一个错误，e 是具体的错误值

简而言之，如果期待一个正确的结果，就返回 Ok，反之则是 Err。

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?

? 跟 unwrap 非常像，但是 ? 会返回一个错误，而不是直接 panic.

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map & and_then

map and and_then 是两个常用的组合器( combinator )，可以用于 Result<T, E> (也可用于 Option<T>).

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类型别名

如果我们要在代码中到处使用 std::result::Result<T, ParseIntError> ，那毫无疑问，代码将变得特别冗长和啰嗦，对于这种情况，可以使用类型别名来解决。

例如在标准库中，就在大量使用这种方式来简化代码: io::Result.

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在 fn main 中使用 Result

一个典型的 main 函数长这样:

fn main() {
    println!("Hello World!");
}

事实上 main 函数还可以返回一个 Result 类型：如果 main 函数内部发生了错误，那该错误会被返回并且打印出一条错误的 debug 信息。

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你可以在这里找到答案(在 solutions 路径下)

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