生命周期注解
A reference has a lifetime, which must not “outlive” the value it refers to. This is verified by the borrow checker.
The lifetime can be implicit - this is what we have seen so far. Lifetimes can also be explicit: &'a Point
, &'document str
. Lifetimes start with '
and 'a
is a typical default name. Read &'a Point
as “a borrowed Point
which is valid for at least the lifetime a
”.
Lifetimes are always inferred by the compiler: you cannot assign a lifetime yourself. Explicit lifetime annotations create constraints where there is ambiguity; the compiler verifies that there is a valid solution.
当考虑向函数传递值和从函数返回值时,生命周期会变得更加复杂。
Speaker Notes
This slide should take about 10 minutes.
In this example, the compiler does not know what lifetime to infer for p3
. Looking inside the function body shows that it can only safely assume that p3
’s lifetime is the shorter of p1
and p2
. But just like types, Rust requires explicit annotations of lifetimes on function arguments and return values.
将 'a
适当添加到 left_most
中:
fn left_most<'a>(p1: &'a Point, p2: &'a Point) -> &'a Point {
这表示.,“假设 p1 和 p2 的存在时间都比 'a
更长,则返回值至少在 'a
内有效”。
在一般情况下,可以省略生命周期,如下一张幻灯片中所述。