Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::comparison_chain: Checks comparison chains written with if that can be rewritten with match and cmp

What it meansChecks comparison chains written with if that can be rewritten with match and cmp. It is in the pedantic group and off by default.

Does it matter?

if is not guaranteed to be exhaustive and conditionals can get repetitive

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

fn f(x: u8, y: u8) {
    if x > y {
        a()
    } else if x < y {
        b()
    } else {
        c()
    }
}

Write this instead

use std::cmp::Ordering;
fn f(x: u8, y: u8) {
     match x.cmp(&y) {
         Ordering::Greater => a(),
         Ordering::Less => b(),
         Ordering::Equal => c()
     }
}

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]
comparison_chain = "warn"

In code

#![warn(clippy::comparison_chain)]

One run

cargo clippy -- -W clippy::comparison-chain

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.

Pedanticgroup

allowdefault level

nofixed by cargo clippy --fix

1.40.0added in Rust

Clippy's own documentation

What it does

Checks comparison chains written with if that can be rewritten with match and cmp.

Why is this bad?

if is not guaranteed to be exhaustive and conditionals can get repetitive

Example

fn f(x: u8, y: u8) {
    if x > y {
        a()
    } else if x < y {
        b()
    } else {
        c()
    }
}

Use instead:

use std::cmp::Ordering;
fn f(x: u8, y: u8) {
     match x.cmp(&y) {
         Ordering::Greater => a(),
         Ordering::Less => b(),
         Ordering::Equal => c()
     }
}

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

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