Suggest use of Option::filter()

[tomers]

What it does

I stumbled upon cases when developers are not familiar enough with all the functions that come with standard libs, such as Option::filter(). Instead, they program that functionality each time, which makes the code much more complex, error prone, and less readable.

Lint Name

filter

Category

style, complexity

Advantage

• Reduces complexity substantially.
• Improves code readability.
• Makes use of lib function instead of coding its functionality in each usage.

Drawbacks

None that I can think of.

Example

match s {
    None => None,
    Some(x) => {
        if x.is_empty() {
            None
        } else {
            Some(x)
        }
    }
}

Could be written as:

s.filter(|x| !x.is_empty())

Full example:

fn bad(s: Option<String>) -> Option<String> {
    match s {
        None => None,
        Some(x) => {
            if x.is_empty() {
                None
            } else {
                Some(x)
            }
        }
    }
}

fn good(s: Option<String>) -> Option<String> {
    s.filter(|x| !x.is_empty())
}

fn main() {
    assert_eq!(bad(None), None);
    assert_eq!(bad(Some("".to_owned())), None);
    assert_eq!(bad(Some("foo".to_owned())), Some("foo".to_owned()));
    assert_eq!(good(None), None);
    assert_eq!(good(Some("".to_owned())), None);
    assert_eq!(good(Some("foo".to_owned())), Some("foo".to_owned()));
}

[kraktus]

@rustbot claim

[kraktus]

Another example while I can think about it

option match {
      Some(x) if cond(x) => x,
      _ => x
}