为什么不需要限定 Option 的 Some 和 None 变体? [英] Why don't Option's Some and None variants need to be qualified?

问题描述

根据文档Option, Option 是一个带有 Some 和 None 变体的枚举.

According to the docs for Option, Option is an enum with variants Some<T> and None.

为什么可以在不限定的情况下引用 Some 和 None ?

Why is it possible to refer to Some and None without qualifying them?

例如，这很好用:

let x = Option::Some(5);
match x {
    Some(a) => println!("Got {}", a),
    None => println!("Got None"),
}

但这无法编译:

enum Foo<T> {
    Bar(T),
    Baz,
}
let x = Foo::Bar(5);
match x {
    Bar(a) => println!("Got {}", a),
    Baz => println!("Got Baz"),
}

来自编译器的错误是unresolved enum variant, struct or const `Bar`

推荐答案

Rustprelude，自动插入到每个源文件中，包含这一行:

The Rust prelude, which is automatically inserted into every source file, contains this line:

pub use option::Option::{self, Some, None};

它带来了 Option 及其范围内的两个变体.

Which brings Option and both its variants in scope.

这篇关于为什么不需要限定 Option 的 Some 和 None 变体?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！