Rust – A hard decision pays off

Re:Rust – A hard decision pays off by Already__Taken on Wednesday August 24, 2022 @08:13PM (#32587641)

Forgive me for asking instead of looking, I'm still getting into rust; why do you map instead of getting the result?

    path.extension().map(|ext| ext == "bundle").unwrap_or(false)

    (path.extension() == "bundle").unwrap_or(false)

or further up

    .map(|e| e.map(|e| e.path()))
    vs
    .map(|e| e.path())

Is the .map keeping any value wrapped in an iterator so you can map again? I thought it was interesting what you wrote looks a lot like what I'd write in powershell.

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Re:Rust – A hard decision pays off by steveklabnik on Wednesday August 24, 2022 @09:47PM (#32588400)

Not your parent, but I do know the answer.

extension() returns an Option<&OsStr>, because not every file has an extension https://doc.rust-lang.org/stable/std/path/struct.Path.html#m...

map on option says "run this closure on the value if it's Some, or do nothing if it's None https://doc.rust-lang.org/stable/std/option/enum.Option.html...

So after the map, we now have an Option<bool>. The unwrap_or method will say "give me the value if it's Some, and give me the argument if it's not https://doc.rust-lang.org/stable/std/option/enum.Option.html...

That means we finally end up with a bool.

  (path.extension() == "bundle").unwrap_or(false)

This code wouldn't work because you're comparing an Option<&OsStr> to a &str. Even if that worked, you'd have a boolean, and unwrap_or doesn't make sense on booleans, you'd just leave off that part.

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Re:Rust – A hard decision pays off by Already__Taken on Monday September 05, 2022 @05:40AM (#32722301)

Awesome thanks, I wasn't on a machine to play around with it at the time.

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Re:Rust – A hard decision pays off by 0x457 on Saturday August 27, 2022 @08:39PM (#32624647)

`extension()` gives you an `Option`, remember `Path` might not be a file or file could be without extension.

Why not `((path.extension() == Some("bundle"))`? I don't know, it didn't work, and I didn't want to spend too much time on it.

`read_dir` gives us an iterator over `Result<DirEntry>`, so `e` in that map is a `Result` and not a `DirEntry`. It's two different "map" functions - on Option<T> and Result<T,E> it maps "T", but on Iterator it maps "Item" from that iterator.

Here is an explanation why `read_dir` give you a Result - https://doc.rust-lang.org/std/fs/fn.read_dir.html#errors

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Re:Rust – A hard decision pays off by Already__Taken on Monday September 05, 2022 @05:39AM (#32722294)

Thanks for the insight

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