Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::manual_slice_size_calculation: When a is &[T], detect a.len() * size_of::<T>() and suggest size_of_val(a) instead

What it meansWhen a is &[T], detect a.len() * size_of::<T>() and suggest size_of_val(a) instead. It is in the complexity group and warns by default.

Does it matter?

Shorter to write Removes the need for the human and the compiler to worry about overflow in the multiplication Potentially faster at runtime as rust emits special no-wrapping flags when it calculates the byte length Less turbofishing

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

let newlen = data.len() * size_of::<i32>();

Write this instead

let newlen = size_of_val(data);

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
manual_slice_size_calculation = "allow"

One run

cargo clippy -- -A clippy::manual-slice-size-calculation

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

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.70.0added in Rust

Clippy's own documentation

What it does

When a is &[T], detect a.len() * size_of::<T>() and suggest size_of_val(a) instead.

Why is this better?

Shorter to write
Removes the need for the human and the compiler to worry about overflow in the multiplication
Potentially faster at runtime as rust emits special no-wrapping flags when it calculates the byte length
Less turbofishing

Example

let newlen = data.len() * size_of::<i32>();

Use instead:

let newlen = size_of_val(data);

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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