Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::manual_bits: usage of `size_of::<T>()` to obtain the size of `T` in bits
What it meansChecks for usage of size_of::<T>() * 8 when T::BITS is available. It is in the style group and warns by default.
What you see
warning: usage of `size_of::<T>()` to obtain the size of `T` in bits --> main.rs:3:1 | 3 | size_of::<usize>() * 8; | ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `usize::BITS as usize` | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_bits = note: `#[warn(clippy::manual_bits)]` on by default
Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.
Does it matter?
Can be written as the shorter T::BITS.
Code that works but is not idiomatic Rust. 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
size_of::<usize>() * 8;
Write this instead
usize::BITS as usize;
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_bits)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
manual_bits = "allow"One run
cargo clippy -- -A clippy::manual-bitsThe [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
Clippy's own documentation
What it does
Checks for usage of size_of::<T>() * 8 when
T::BITS is available.
Why is this bad?
Can be written as the shorter T::BITS.
Example
size_of::<usize>() * 8;
Use instead:
usize::BITS as usize;
Configuration
-
msrv: The minimum rust version that the project supports. Defaults to therust-versionfield inCargo.toml(default:
current version)
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- needless_returnunneeded `return` statement
- new_without_defaultChecks for public types with a pub fn new() -> Self method and no implementation of Default
- len_zeroChecks for getting the length of something via .len() just to compare to zero, and suggests using .is_empty() where applicable
- let_unit_valuethis let-binding has unit value
- main_recursionrecursing into entrypoint `main`
- manual_async_fnthis function can be simplified using the `async fn` syntax
- manual_dangling_ptrmanual creation of a dangling pointer
- manual_is_ascii_checkmanual check for common ascii range
- manual_is_finiteChecks for manual is_finite reimplementations (i.e., x != <float>::INFINITY && x != <float>::NEG_INFINITY)
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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