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Update ch19-02-advanced-lifetimes.md

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@ -170,7 +170,7 @@ note: but the referenced data is only valid for the lifetime 's as defined on th
Rust 并不知道 `'c` 和 `'s` 之间的关系. `Context`中被引用的数据的生命周期是`'s`, 对`Context`的引用有生命周期`'c`, 为了让代码有效, 需要保证生命周期 `'s` 比生命周期 `'c` 更长. 如果 `'s` 存活的时间没有 `'c` 长, 那么对 `Context` 的引用可能就要出问题. Rust 并不知道 `'c` 和 `'s` 之间的关系. `Context`中被引用的数据的生命周期是`'s`, 对`Context`的引用有生命周期`'c`, 为了让代码有效, 需要保证生命周期 `'s` 比生命周期 `'c` 更长. 如果 `'s` 存活的时间没有 `'c` 长, 那么对 `Context` 的引用可能就要出问题.
现在就让我们来看这一节: Rust 有一个被称为*生命周期子类型(lifetime subtyping)*的特性, 它可以指明一个生命周期参数的存活时间不会比另一个生命周期短. In the angle brackets where we declare lifetime 本节就是为了解决这个问题: Rust 有一个被称为 *生命周期子类型 (lifetime subtyping)* 的特性, 它可以指明一个生命周期参数的存活时间不会比另一个生命周期短. In the angle brackets where we declare lifetime
parameters, we can declare a lifetime `'a` as usual, and declare a lifetime parameters, we can declare a lifetime `'a` as usual, and declare a lifetime
`'b` that lives at least as long as `'a` by declaring `'b` with the syntax `'b: `'b` that lives at least as long as `'a` by declaring `'b` with the syntax `'b:
'a`. 'a`.