rust-course/writing_material/lifetime_elision_rules.md

一些lifetime消除规则

1

Let's talk about a feature that's available in both editions: we've added some additional elision rules for impl blocks and function definitions. Code like this:

impl<'a> Reader for BufReader<'a> {
    // methods go here
}

can now be written like this:

impl Reader for BufReader<'_> {
    // methods go here
}

The '_ lifetime still shows that BufReader takes a parameter, but we don't need to create a name for it anymore.

2

Lifetimes are still required to be defined in structs. However, we no longer require as much boilerplate as before:

// Rust 2015
struct Ref<'a, T: 'a> {
    field: &'a T
}

// Rust 2018
struct Ref<'a, T> {
    field: &'a T
}

The : 'a is inferred. You can still be explicit if you prefer. We're considering some more options for elision here in the future, but have no concrete plans yet.