Structs that borrow in Rust

A struct holding a reference carries a lifetime, tying it to the data it reads.

struct Header<'a> {
    name: &'a str,
    value: &'a str,
}

impl<'a> Header<'a> {
    fn parse(line: &'a str) -> Option<Header<'a>> {
        let (name, value) = line.split_once(": ")?;
        Some(Header { name, value })
    }
}

fn main() {
    let raw = String::from("Content-Type: text/html");
    if let Some(header) = Header::parse(&raw) {
        println!("{} = {}", header.name, header.value);
    }
    println!("{:?}", Header::parse("nonsense").is_none());
}

How it works

1. The lifetime is declared on the struct and used on the field.
2. The struct cannot outlive the text it points into.
3. This is how zero-copy parsers avoid allocating.

Keywords and builtins used here

• Header
• Option
• Some
• String
• fn
• if
• impl
• let
• main
• parse
• str
• struct

The run, in numbers

Lines

19

Characters to type

415

Tokens

150

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 86 seconds.

Type this snippet

Step 2 of 4 in Lifetime annotations, step 2 of 11 in Lifetimes & interior mutability.

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