Nibbles of Rust – Restructuring Patterns

Re:Nibbles of Rust – Restructuring Patterns by rtpg on Sunday April 16, 2023 @09:31AM (#35589893)

What I want is..

let MyEnum(foo, bar, baz) = input but otherwise { do some stuff return some value }

Point being I don’t have to check for MyEnum-ness twice (like with matches! + if let) and the indented code is for the exception (no match) not the norm.

Tho I … guess !matches(MyEnum{ .. }) is not the worst… but it’s annoying to have this pattern all over my code instead of as some encoded concept we all use

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Re:Nibbles of Rust – Restructuring Patterns by ljsb on Sunday April 16, 2023 @09:44AM (#35589974)

You were pretty close with your hypothetical syntax! You can write:

  let Some(y) = x else { do_stuff(); return };

I think it was a fairly recent addition to Rust.

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Re:Nibbles of Rust – Restructuring Patterns by rtpg on Sunday April 16, 2023 @09:51AM (#35590027)

Thank dog for that. I feel like I even read the release notes for that but it was while I hadn’t been touching a specific codebase with loads of early returns. Thanks for pointing this out!

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Re:Nibbles of Rust – Restructuring Patterns by chrismorgan on Sunday April 16, 2023 @09:53AM (#35590045)

let-else was stabilised in 1.65.0, released 2022-11-03.

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Re:Nibbles of Rust – Restructuring Patterns by metadat on Sunday April 16, 2023 @02:29PM (#35592840)

What determines whether `let Some(y) = x` evaluates to boolean true?

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Re:Nibbles of Rust – Restructuring Patterns by asherah on Sunday April 16, 2023 @02:47PM (#35593067)

if x is `Some`, then `y` is set to the inner value and the following block occurs. you can also use this with other enums - i don't remember off the top of my head if it works for all enums, but you can at least also use it with `Result`

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Re:Nibbles of Rust – Restructuring Patterns by jeffdn on Sunday April 16, 2023 @06:38PM (#35594871)

It absolutely works for all patterns!

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Re:Nibbles of Rust – Restructuring Patterns by bombela on Sunday April 16, 2023 @02:52PM (#35593126)

The fact that the pattern matches.

Here the type being matched is:

    enum Option<T> {
        None,
        Some(T)
    }

    let x = Some(42);
    let Some(y) = x else { panic!("None") };

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