14th Jan 2022

Rust 1.58.0 Release Notes

std::fmt Documentation

The Rust 1.58.0 update today bought a very nice addition, this is a feature that’s often missed by the growing number of dynamic language users that are giving Rust a try, and it’s now available in stable!

It allows you to put variables from the outside scope directly into format string curly braces:

// In all examples below x = "world"
let x = "world";
println!("Hello {x}!");

Hello world!

You can also use format specifiers within the curly braces.

For example with debug output:

let items = vec![10, 20, 30];
println!("{items:?}")

[10, 20, 30]

Or pretty print the output:

println!("{items:#?}")

[
    10,
    20,
    30,
]

If you haven’t seen it before, you can set the minimum width of how items are printed to give uniform spacing with :[width]. Example to print a table with even spacing:

let items = ["these", "words", "are", "different", "sizes"];
let column1 = "item";
let column2 = "iter";
println!("{column1:10}| {column2}");
println!("----------------");
for (i, item) in items.iter().enumerate() {
	println!("{item:10}: {i}");
}

item      | iter
----------------
these     : 0
words     : 1
are       : 2
different : 3
sizes     : 4

Align items t