Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::return_and_then: use the `?` operator instead of an `and_then` call

What it meansDetect functions that end with Option::and_then or Result::and_then, and suggest using the ? operator instead. It is in the restriction group and off by default.

What you see

warning: use the `?` operator instead of an `and_then` call
  --> main.rs:4:5
   |
 4 | /     opt.and_then(|n| {
 5 | |         if n > 1 {
 6 | |             Some(n + 1)
 7 | |         } else {
...  |
10 | |     })
   | |______^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#return_and_then
   = note: requested on the command line with `-W clippy::return-and-then`
help: try
   |
 4 ~     let n = opt?;
 5 +     if n > 1 {
 6 +                 Some(n + 1)
 7 +             } else {
 8 +                 None
 9 +            }
   |

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

The and_then method is used to chain a computation that returns an Option or a Result. This can be replaced with the ? operator, which is more concise and idiomatic.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

fn test(opt: Option<i32>) -> Option<i32> {
    opt.and_then(|n| {
        if n > 1 {
            Some(n + 1)
        } else {
            None
       }
    })
}

Write this instead

fn test(opt: Option<i32>) -> Option<i32> {
    let n = opt?;
    if n > 1 {
        Some(n + 1)
    } else {
        None
    }
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
return_and_then = "warn"

In code

#![warn(clippy::return_and_then)]

One run

cargo clippy -- -W clippy::return-and-then

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Restrictiongroup

allowdefault level

yesfixed by cargo clippy --fix

1.86.0added in Rust

Clippy's own documentation

What it does

Detect functions that end with Option::and_then or Result::and_then, and suggest using the ? operator instead.

Why is this bad?

The and_then method is used to chain a computation that returns an Option or a Result. This can be replaced with the ? operator, which is more concise and idiomatic.

Example

fn test(opt: Option<i32>) -> Option<i32> {
    opt.and_then(|n| {
        if n > 1 {
            Some(n + 1)
        } else {
            None
       }
    })
}

Use instead:

fn test(opt: Option<i32>) -> Option<i32> {
    let n = opt?;
    if n > 1 {
        Some(n + 1)
    } else {
        None
    }
}

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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