clippy::manual_option_as_slice: This detects various manual reimplementations of Option::as_slice

Does it matter?

Those implementations are both more complex than calling as_slice and unlike that incur a branch, pessimizing performance and leading to more generated code.

Code that does something simple in a complicated way. Warns by default.

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

_ = opt.as_ref().map_or(&[][..], std::slice::from_ref);
_ = match opt.as_ref() {
    Some(f) => std::slice::from_ref(f),
    None => &[],
};

Write this instead

_ = opt.as_slice();
_ = opt.as_slice();

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

#[allow(clippy::manual_option_as_slice)]
fn my_function() { /* ... */ }

[lints.clippy]
manual_option_as_slice = "allow"

cargo clippy -- -A clippy::manual-option-as-slice

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