[FIXED] What does <'_> mean in Rust?

Issue

In this code from Debug examples:

use std::fmt;

struct Point {
    x: i32,
    y: i32,
}

impl fmt::Debug for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Point")
         .field("x", &self.x)
         .field("y", &self.y)
         .finish()
    }
}

let origin = Point { x: 0, y: 0 };

assert_eq!(format!("The origin is: {origin:?}"), "The origin is: Point { x: 0, y: 0 }");

What does <'_> mean in f: &mut fmt::Formatter<'_>?

Solution

The ' denotes that it is a Lifetime: https://doc.rust-lang.org/rust-by-example/scope/lifetime.html

This is usually written as 'a where a is the name of the lifetime (like the name of the variable, can be any name)

The _ means that the compiler can infer the name/type. (so you don't have to figure it out, makes it easier) You can find more info here: https://stackoverflow.com/a/37215830/2037998

The <> is because of Generics. You can see that in the docs it is defines as impl<'a> Formatter<'a>

Answered By - Ralph Bisschops

Answer Checked By - Robin (PHPFixing Admin)