lifetime operator.md

Lifetime Operator

// params with two lifetime as generic. Return depends only on first param's lifetime.
fn skip_prefix<'a, 'b>(line: &'a str, prefix: &'b str) -> &'a str {
    // ...
}

// Perfectly handles this case
fn skip_prefix(line: &str, prefix: &str) -> &str {
    // ...
}

let line = "lang:en=Hello World!";
let lang = "en";
let v;
{
    let p = format!("lang:{}=", lang);  // -+ `p` comes into scope.
    v = skip_prefix(line, p.as_str());  //  |
}                                       // -+ `p` goes out of scope.
println!("{}", v);

// struct usage
// To ensure that any reference to a Foo cannot outlive the reference to an i32 it contains.

struct Foo<'a> {
    x: &'a i32,
}

// Named lifetimes are a way of giving these scopes a name. Giving something a name is the first step towards being able to talk about it.

// static lifetime
let x: &'static str = "Hello, world.";
static FOO: i32 = 5;
let x: &'static i32 = &FOO;

Lifetime Elision

The rules for lifetime elision are as follows:

• In a function's arguments, every elided lifetime becomes a separate lifetime parameter.
• If there is only one input lifetime, it is used for all the elided lifetimes in the return values of the function.
• If there are multiple input lifetimes, and one of them is &self or &mut self, the lifetime of self is used for all the elided output lifetimes.