suggest map_or for simple None substitutions

[matthiaskrgr]

What it does

Find patterns like

pub fn a(s: Option<String>) -> usize {
    match s {
        Some(string) => string.len(),
        None => 1, 
    }
}

and suggest to use map_or instead:

pub fn a(s: Option<String>) -> usize {
    s.map_or(1, |string| string.len())
}

We might need to consider restricting such a lint to simple matches that don't have a lot of "stuff going on"

Lint Name

map_or_match? matching_map_or? mmh

Category

style

Advantage

for simple matches, this reduces lines from 4 to 1, and I think it's a bit easier to grasp what is going on if you are familiar with map_or.

Drawbacks

🤷

We might want to bail out on matches where a single arm spans several lines.

Example

pub fn a(s: Option<String>) -> usize {
    match s {
        Some(string) => string.len(),
        None => 1, 
    }
}

Could be written as:

pub fn a(s: Option<String>) -> usize {
    s.map_or(1, |string| string.len())
}

[Jarcho]

Just a note for anyone taking this. There is option_if_let_some_else_none which covers this only for if let ... else ....

[J-ZhengLi]

Seems like this hasn't been fixed yet... @rustbot claim