Wednesday, 4 August 2021

Tinkering with Rust - an underscore

Whilst tinkering with the Kata Containers kata-agent component, I was trying to work out what the underscore meant in this line of code: -

let _ =;

Thankfully, this GitHub issue: -

Documet let _ = ... behavior saliently, or even warn about it #40096

led me to this section of the Rust language book: -

Ignoring Values in a Pattern

You’ve seen that it’s sometimes useful to ignore values in a pattern, such as in the last arm of a match, to get a catchall that doesn’t actually do anything but does account for all remaining possible values. There are a few ways to ignore entire values or parts of values in a pattern: using the _ pattern (which you’ve seen), using the _ pattern within another pattern, using a name that starts with an underscore, or using .. to ignore remaining parts of a value. Let’s explore how and why to use each of these patterns.

and: -

We’ve used the underscore (_) as a wildcard pattern that will match any value but not bind to the value. Although the underscore _ pattern is especially useful as the last arm in a match expression, we can use it in any pattern, including function parameters, as shown in Listing 18-17.

Ignoring an Entire Value with _

No comments:

Yay, VMware Fusion and macOS Big Sur - no longer "NAT good friends" - forgive the double negative and the terrible pun ...

After macOS 11 Big Sur was released in 2020, VMware updated their Fusion product to v12 and, sadly, managed to break Network Address Trans...