Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::if_then_some_else_none: Checks for if-else that could be written using either bool::then or bool::then_some

What it meansChecks for if-else that could be written using either bool::then or bool::then_some. It is in the restriction group and off by default.

Does it matter?

Looks a little redundant. Using bool::then is more concise and incurs no loss of clarity. For simple calculations and known values, use bool::then_some, which is eagerly evaluated in comparison to bool::then.

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

let a = if v.is_empty() {
    println!("true!");
    Some(42)
} else {
    None
};

Write this instead

let a = v.is_empty().then(|| {
    println!("true!");
    42
});

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]
if_then_some_else_none = "warn"

In code

#![warn(clippy::if_then_some_else_none)]

One run

cargo clippy -- -W clippy::if-then-some-else-none

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.

Settings in clippy.toml

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

Restrictiongroup

allowdefault level

yesfixed by cargo clippy --fix

1.53.0added in Rust

Clippy's own documentation

What it does

Checks for if-else that could be written using either bool::then or bool::then_some.

Why restrict this?

Looks a little redundant. Using bool::then is more concise and incurs no loss of clarity. For simple calculations and known values, use bool::then_some, which is eagerly evaluated in comparison to bool::then.

Example

let a = if v.is_empty() {
    println!("true!");
    Some(42)
} else {
    None
};

Could be written:

let a = v.is_empty().then(|| {
    println!("true!");
    42
});

Configuration

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

(default: current version)

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

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