Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::size_of_in_element_count: Detects expressions where size_of::<T> or size_of_val::<T> is used as a count of elements of type T

What it meansDetects expressions where size_of::<T> or size_of_val::<T> is used as a count of elements of type T It is in the correctness group and denied by default (the build fails).

Does it matter?

These functions expect a count of T and not a number of bytes

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

const SIZE: usize = 128;
let x = [2u8; SIZE];
let mut y = [2u8; SIZE];
unsafe { copy_nonoverlapping(x.as_ptr(), y.as_mut_ptr(), size_of::<u8>() * SIZE) };

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
size_of_in_element_count = "allow"

One run

cargo clippy -- -A clippy::size-of-in-element-count

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.

Correctnessgroup

denydefault level

nofixed by cargo clippy --fix

1.50.0added in Rust

Clippy's own documentation

What it does

Detects expressions where size_of::<T> or size_of_val::<T> is used as a count of elements of type T

Why is this bad?

These functions expect a count of T and not a number of bytes

Example

const SIZE: usize = 128;
let x = [2u8; SIZE];
let mut y = [2u8; SIZE];
unsafe { copy_nonoverlapping(x.as_ptr(), y.as_mut_ptr(), size_of::<u8>() * SIZE) };

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

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