this post was submitted on 21 Apr 2024

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since: my first project (codeberg.org)

submitted 6 months ago* (last edited 6 months ago) by larix to c/rust

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This is my first project in rust, called: since. A small tool to filter logfiles or any other files with a timestamp in it, by a given timestamp.

For example:

since 1h /var/log/messages prints all lines from the last hour. since 00:00 /var/log/messages prints all lines since 00:00.

It would be nice if you could take a look at the code. What would you change, what should I change?

I’m not a professional programmer, this is just a hobby, but I want to learn as much as possible.

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[–] [email protected] 22 points 6 months ago* (last edited 6 months ago) (2 children)

I took a very quick look at the code and one thing I noticed, is that you're using &String.

For a parameter in a function, you always want to use &str instead, as explained here: https://doc.rust-lang.org/book/ch04-03-slices.html#string-slices-as-parameters

I believe, it's also not a thing to return &String (nor to store it in a struct). I don't have as solid of an explanation for it, it's just not something I see much in Rust code (and in the chapter above, they do use a &str as return value, too).
Maybe someone else can weigh in on that.

The same applies for:

&[] rather than &Vec
&Path rather than &PathBuf
&OsStr rather than &OsString

I would also recommend using Clippy. I think, you can just run cargo clippy and it'll work.
It's a linter and will tell you lots of code style issues (like using &String as a parameter).
If you've never run it, it might spit out a lot of warnings at first, but working through them can teach you quite some things.

[–] larix 8 points 6 months ago* (last edited 6 months ago) (2 children)

Thank you very much. I’ll change it. I did run cargo clippy, but it didn’t complained anything anymore before I published the code. 🙂

One question to return value Option<&String>:

is it better to change to Option<&str> or &Option<String> if the value in the struct is a Option<String>? The latter sounds more logical to me.

[–] [email protected] 7 points 6 months ago (1 children)

@larix @Ephera it's better to return an Option<&str> as a String may DeRef to &str.

For example

self.name.as_deref()

[–] [email protected] 2 points 6 months ago (2 children)

Hmm, interesting. The documentation tells me, it creates a new Option value, and allocating memory every time someone just wants to look at a value could be pretty bad.

But I guess, an Option of a reference never needs to allocate memory, because it'll either be a pointer to a value (Some) or a pointer to null (None). Right?

Well, that explains why it's technically possible.
As for why Option<&str> is preferrable then:
It hides away your internals. Your caller should only care whether they can get the value or not (Some vs. None), not what the precise reason is. That reason or your internal structure might change.

@larix

[–] larix 3 points 6 months ago

Well, that explains why it's technically possible.

As for why Option<&str> is preferrable then: It hides away your internals. Your caller should only care whether they can get the value or not (Some vs. None), not what the precise reason is. That reason or your internal structure might change.

Yes, that makes sense too. Great!

I’ve updated the code as recommended.

@[email protected] @[email protected]

[–] [email protected] 3 points 6 months ago

Hmm, not quite sure why Clippy didn't say anything then. I think, it was a Option<&String> which I had seen as a parameter type. Maybe it doesn't complain when it's wrapped in an Option...

[–] ExperimentalGuy 2 points 6 months ago

Thanks, that was a lot of info I didn't know either. I was wondering how to use clippy...

[–] [email protected] 13 points 6 months ago (1 children)

Very neat idea!

[–] larix 4 points 6 months ago

Thanks!