2017-03-13 23:27:01 +08:00
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< ul class = "chapter" > < li > < a href = "ch01-00-introduction.html" > < strong > 1.< / strong > 介绍< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch01-01-installation.html" > < strong > 1.1.< / strong > 安装< / a > < / li > < li > < a href = "ch01-02-hello-world.html" > < strong > 1.2.< / strong > Hello, World!< / a > < / li > < / ul > < / li > < li > < a href = "ch02-00-guessing-game-tutorial.html" > < strong > 2.< / strong > 猜猜看教程< / a > < / li > < li > < a href = "ch03-00-common-programming-concepts.html" > < strong > 3.< / strong > 通用编程概念< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch03-01-variables-and-mutability.html" > < strong > 3.1.< / strong > 变量和可变性< / a > < / li > < li > < a href = "ch03-02-data-types.html" > < strong > 3.2.< / strong > 数据类型< / a > < / li > < li > < a href = "ch03-03-how-functions-work.html" > < strong > 3.3.< / strong > 函数如何工作< / a > < / li > < li > < a href = "ch03-04-comments.html" > < strong > 3.4.< / strong > 注释< / a > < / li > < li > < a href = "ch03-05-control-flow.html" > < strong > 3.5.< / strong > 控制流< / a > < / li > < / ul > < / li > < li > < a href = "ch04-00-understanding-ownership.html" > < strong > 4.< / strong > 认识所有权< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch04-01-what-is-ownership.html" > < strong > 4.1.< / strong > 什么是所有权< / a > < / li > < li > < a href = "ch04-02-references-and-borrowing.html" > < strong > 4.2.< / strong > 引用 & 借用< / a > < / li > < li > < a href = "ch04-03-slices.html" > < strong > 4.3.< / strong > Slices< / a > < / li > < / ul > < / li > < li > < a href = "ch05-00-structs.html" > < strong > 5.< / strong > 结构体< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch05-01-method-syntax.html" > < strong > 5.1.< / strong > 方法语法< / a > < / li > < / ul > < / li > < li > < a href = "ch06-00-enums.html" > < strong > 6.< / strong > 枚举和模式匹配< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch06-01-defining-an-enum.html" > < strong > 6.1.< / strong > 定义枚举< / a > < / li > < li > < a href = "ch06-02-match.html" > < strong > 6.2.< / strong > < code > match< / code > 控制流运算符< / a > < / li > < li > < a href = "ch06-03-if-let.html" > < strong > 6.3.< / strong > < code > if let< / code > 简单控制流< / a > < / li > < / ul > < / li > < li > < a href = "ch07-00-modules.html" > < strong > 7.< / strong > 模块< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch07-01-mod-and-the-filesystem.html" > < strong > 7.1.< / strong > < code > mod< / code > 和文件系统< / a > < / li > < li > < a href = "ch07-02-controlling-visibility-with-pub.html" > < strong > 7.2.< / strong > 使用< code > pub< / code > 控制可见性< / a > < / li > < li > < a href = "ch07-03-importing-names-with-use.html" > < strong > 7.3.< / strong > 使用< code > use< / code > 导入命名< / a > < / li > < / ul > < / li > < li > < a href = "ch08-00-common-collections.html" > < strong > 8.< / strong > 通用集合类型< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch08-01-vectors.html" > < strong > 8.1.< / strong > vector< / a > < / li > < li > < a href = "ch08-02-strings.html" > < strong > 8.2.< / strong > 字符串< / a > < / li > < li > < a href = "ch08-03-hash-maps.html" > < strong > 8.3.< / strong > 哈希 map< / a > < / li > < / ul > < / li > < li > < a href = "ch09-00-error-handling.html" > < strong > 9.< / strong > 错误处理< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch09-01-unrecoverable-errors-with-panic.html" > < strong > 9.1.< / strong > < code > panic!< / code > 与不可恢复的错误< / a > < / li > < li > < a href = "ch09-02-recoverable-errors-with-result.html" > < strong > 9.2.< / strong > < code > Result< / code > 与可恢复的错误< / a > < / li > < li > < a href = "ch09-03-to-panic-or-not-to-panic.html" > < strong > 9.3.< / strong > < code > panic!< / code > 还是不< code > panic!< / code > < / a > < / li > < / ul > < / li > < li > < a href = "ch10-00-generics.html" > < strong > 10.< / strong > 泛型、trait 和生命周期< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch10-01-syntax.html" > < strong > 10.1.< / strong > 泛型数据类型< / a > < / li > < li > < a href = "ch10-02-traits.html" > < strong > 10.2.< / strong > trait： < / a > < / li > < li > < a href = "ch10-03-lifetime-syntax.html" > < strong > 10.3.< / strong > 生命周期与引用有效性< / a > < / li > < / ul > < / li > < li > < a href = "ch11-00-testing.html" > < strong > 11.< / strong > 测试< / a > < / li > < li > < ul class = "section" > < li > < a href = "ch11-01-writing-tests.html" > < strong > 11.1.< / strong > 编写测试< / a > < / li > < li > < a href = "ch11-02-running-tests.html" > < strong > 11.2.< / strong > 运行测试< / a > < / li > < li > < a href = "ch11-03-test-organization.html" > < strong > 11.3.< / strong > 测试的组织结构< / a > < / li > < / ul > < / li > < li > < a href = "ch12-00-an-io-project.h
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2017-03-16 00:02:13 +08:00
< a class = "header" href = "#refcellt和内部可变性模式" name = "refcellt和内部可变性模式" > < h2 > < code > RefCell< T> < / code > 和内部可变性模式< / h2 > < / a >
< blockquote >
< p > < a href = "https://github.com/rust-lang/book/blob/master/second-edition/src/ch15-05-interior-mutability.md" > ch15-05-interior-mutability.md< / a >
< br >
commit 3f2a1bd8dbb19cc48b210fc4fb35c305c8d81b56< / p >
< / blockquote >
< p > < strong > 内部可变性< / strong > （ < em > Interior mutability< / em > ）是 Rust 中的一个设计模式，它允许你即使在有不可变引用时改变数据，这通常是借用规则所不允许。内部可变性模式涉及到在数据结构中使用< code > unsafe< / code > 代码来绕过 Rust 通常的可变性和借用规则。我们还未讲到不安全代码；第十九章会学习他们。内部可变性模式用于当你可以确保代码在运行时也会遵守借用规则，哪怕编译器也不能保证的情况。引入的< code > unsafe< / code > 代码将被封装进安全的 API 中，而外部类型仍然是不可变的。< / p >
< p > 让我们通过遵循内部可变性模式的< code > RefCell< T> < / code > 类型来开始探索。< / p >
< a class = "header" href = "#refcellt拥有内部可变性" name = "refcellt拥有内部可变性" > < h3 > < code > RefCell< T> < / code > 拥有内部可变性< / h3 > < / a >
< p > 不同于< code > Rc< T> < / code > ， < code > RefCell< T> < / code > 代表其数据的唯一的所有权。那么是什么让< code > RefCell< T> < / code > 不同于像< code > Box< T> < / code > 这样的类型呢？回忆一下第四章所学的借用规则：< / p >
< ol >
< li > 在任意给定时间，< strong > 只能< / strong > 拥有如下中的一个：< / li >
< / ol >
< ul >
< li > 一个可变引用。< / li >
< li > 任意属性的不可变引用。< / li >
< / ul >
< ol start = "2" >
< li > 引用必须总是有效的。< / li >
< / ol >
< p > 对于引用和< code > Box< T> < / code > ，借用规则的不可变性作用于编译时。对于< code > RefCell< T> < / code > ，这些不可变性作用于< strong > 运行时< / strong > 。对于引用，如果违反这些规则，会得到一个编译错误。而对于< code > RefCell< T> < / code > ，违反这些规则会< code > panic!< / code > 。< / p >
< p > Rust 编译器执行的静态分析时天生保守的。代码的一些属性则不可能通过分析代码发现：其中最著名的就是停机问题（停机问题），这超出了本书的范畴，不过如果你感兴趣的话这是一个值得研究的有趣主题。< / p >
< p > 因为一些分析是不可能的， < code > RefCell< T> < / code > 正是用于当你知道代码遵守借用规则，而编译器不能理解的时候。< / p >
< p > 类似于< code > Rc< T> < / code > ， < code > RefCell< T> < / code > 只能用于单线程场景。在并发章节会介绍如何在多线程程序中使用< code > RefCell< T> < / code > 的功能。现在所有你需要知道的就是如果尝试在多线程上下文中使用< code > RefCell< T> < / code > ，会得到一个编译错误。< / p >
< p > 对于引用，可以使用< code > & < / code > 和< code > & mut< / code > 语法来分别创建不可变和可变的引用。不过对于< code > RefCell< T> < / code > ，我们使用< code > borrow< / code > 和< code > borrow_mut< / code > 方法，它是< code > RefCell< T> < / code > 拥有的安全 API 的一部分。< code > borrow< / code > 返回< code > Ref< / code > 类型的智能指针，而< code > borrow_mut< / code > 返回< code > RefMut< / code > 类型的智能指针。这两个类型实现了< code > Deref< / code > 所以可以被当作常规引用处理。< code > Ref< / code > 和< code > RefMut< / code > 动态的借用所有权，而他们的< code > Drop< / code > 实现也动态的释放借用。< / p >
2017-03-13 23:27:01 +08:00
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