From 8073e9b9c860904cce3dda523dd0e5a00dd27928 Mon Sep 17 00:00:00 2001 From: Zheng Ping Date: Wed, 12 Jul 2017 22:32:49 +0800 Subject: [PATCH] Update ch19-02-advanced-lifetimes.md --- src/ch19-02-advanced-lifetimes.md | 24 ++++-------------------- 1 file changed, 4 insertions(+), 20 deletions(-) diff --git a/src/ch19-02-advanced-lifetimes.md b/src/ch19-02-advanced-lifetimes.md index 0ec6b65..efd2df5 100644 --- a/src/ch19-02-advanced-lifetimes.md +++ b/src/ch19-02-advanced-lifetimes.md @@ -103,33 +103,17 @@ body at 15:55... fn parse(&self) -> Result<(), &str> { ``` -还记得生命周期的省略规则吗? If we annotate the lifetimes of the references, the -signature would be: +还记得生命周期的省略规则吗? 如果我们注解引用的生命周期, 那么可以这样写: ```rust,ignore fn parse<'a>(&'a self) -> Result<(), &'a str> { ``` -That is, the error part of the return value of `parse` has a lifetime that is -tied to the `Parser` instance's lifetime (that of `&self` in the `parse` method -signature). That makes sense, as the returned string slice references the -string slice in the `Context` instance that the `Parser` holds, and we've -specified in the definition of the `Parser` struct that the lifetime of the -reference to `Context` that `Parser` holds and the lifetime of the string slice -that `Context` holds should be the same. +也就是说, `parse`函数返回值的错误中的部分是因为它有一个生命周期被绑定到了`Parser`实例的生命周期上面(也就是`parse`方法中的`&self`). 这就是了, 因为被返回的字符串切片引用了`Parser`持有的`Context`实例中的字符串切片, 并且我们已经在`Parser`结构的定义中指定了`Parser`中的`Context`的引用的生命周期和`Context`持有的字符串切片的生命周期是一样的. -The problem is that the `parse_context` function returns the value returned -from `parse`, so the lifetime of the return value of `parse_context` is tied to -the lifetime of the `Parser` as well. But the `Parser` instance created in the -`parse_context` function won't live past the end of the function (it's -temporary), and the `context` will go out of scope at the end of the function -(`parse_context` takes ownership of it). +问题是`parse_context`函数要返回`parse`方法的返回值, 这样`parse_context`的返回值的生命周期也就被绑定到了`Parser`的生命周期上了. 但是在`parse_context`函数中创建的`Parser`实例在函数结束后就不会存活了(它是临时的), 并且`context`在函数结束后也会越过作用域(`parse_context`拥有它的所有权). -We're not allowed to return a reference to a value that goes out of scope at -the end of the function. Rust thinks that's what we're trying to do because we -annotated all the lifetimes with the same lifetime parameter. That told Rust -the lifetime of the string slice that `Context` holds is the same as that of -the lifetime of the reference to `Context` that `Parser` holds. +我们不能返回只在函数作用域内才能存活的值的引用. Rust就认为我们在做这个事情, 因为我们把所有的生命周期参数都注解成一样的了. 这就告诉 Rust `Context`持有的字符串切片的生命周期和`Parser`持有的`Context`引用的生命周期是一样的. The `parse_context` function can't see that within the `parse` function, the string slice returned will outlive both `Context` and `Parser`, and that the