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| -rw-r--r-- | src/doc/trpl/lifetimes.md | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/src/doc/trpl/lifetimes.md b/src/doc/trpl/lifetimes.md index 11d651c5778..8e02367b921 100644 --- a/src/doc/trpl/lifetimes.md +++ b/src/doc/trpl/lifetimes.md @@ -101,6 +101,8 @@ the lifetime `'a` has snuck in between the `&` and the `mut i32`. We read `&mut i32` as ‘a mutable reference to an i32’ and `&'a mut i32` as ‘a mutable reference to an `i32` with the lifetime `'a`’. +# In `struct`s + You’ll also need explicit lifetimes when working with [`struct`][structs]s: ```rust @@ -137,6 +139,33 @@ x: &'a i32, uses it. So why do we need a lifetime here? We need to ensure that any reference to a `Foo` cannot outlive the reference to an `i32` it contains. +## `impl` blocks + +Let’s implement a method on `Foo`: + +```rust +struct Foo<'a> { + x: &'a i32, +} + +impl<'a> Foo<'a> { + fn x(&self) -> &'a i32 { self.x } +} + +fn main() { + let y = &5; // this is the same as `let _y = 5; let y = &_y;` + let f = Foo { x: y }; + + println!("x is: {}", f.x()); +} +``` + +As you can see, we need to declare a lifetime for `Foo` in the `impl` line. We repeat +`'a` twice, just like on functions: `impl<'a>` defines a lifetime `'a`, and `Foo<'a>` +uses it. + +## Multiple lifetimes + If you have multiple references, you can use the same lifetime multiple times: ```rust |