Rust 2021版计划于10月发布，将带来哪些新特性？

{"type":"doc","content":[{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Rust 语言的第三版，即 Rust 2021，计划在 10 月发布。Rust 2021 包含了一些微小的变化，尽管如此，在实际应用中，它们仍有望显著改善 Rust 的感觉。"}]}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"什么是版本？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"作为 Rust 的更新原则， Rust1.0 的发布确立了一个“"},{"type":"link","attrs":{"href":"https:\/\/blog.rust-lang.org\/2014\/10\/30\/Stability.html","title":null,"type":null},"content":[{"type":"text","text":"稳定前进"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"”（stability without stagnation）。从 1.0 版本开始，Rust 的规则是，一旦某个特性在稳定版上发布，我们将保证在以后的所有版本中都支持它。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"但是，有些时候，能够对语言做一些不向后兼容的小改动是很有用的。一个显而易见的例子是引入一个新的关键字，它会使同名变量无效。比如，Rust 的第一个版本中就没有 "},{"type":"codeinline","content":[{"type":"text","text":"async"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 和 "},{"type":"codeinline","content":[{"type":"text","text":"await"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 这两个关键字。如果这些关键字在以后的版本中突然变成关键字，那么就会破坏类似 "},{"type":"codeinline","content":[{"type":"text","text":"let async = 1;"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 的代码。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}},{"type":"strong"}],"text":"版本"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"就是我们解决这个问题的机制。当我们想要发布一个本来是向后不兼容的特性时，我们就把它作为新的 Rust 版本的一部分。版本是可以选择的，因此现有包（crate）不会看到这些更改，除非明确地将其迁移到新版本上。这就是说，除非选择 2018 版或更新版本，即使是最新版本的 Rust 也不会把 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的，这是因为"},{"type":"link","attrs":{"href":"https:\/\/doc.rust-lang.org\/book\/ch05-03-method-syntax.html#wheres-the---operator","title":null,"type":null},"content":[{"type":"text","text":"方法调用语法是如何工作"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"的。增加 trait 实现会改变这个含义。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"一般情况下，我们将这种破坏（增加特性的实现） 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不会将单个参数处理为格式字符串。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Rust 2021 采用了一个更加一致的 "},{"type":"codeinline","content":[{"type":"text","text":"panic!()"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 宏，以避免出现这种混乱的情况。全新 "},{"type":"codeinline","content":[{"type":"text","text":"panic!()"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 宏将不再接受任意的表达式作为唯一参数。它将像 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