Clippy lints / Suspicious
Clippy lint · Suspicious · checked with Clippy 0.1.99
clippy::cast_enum_truncation: casting `main::E::X` to `u8` will truncate the value
What it meansChecks for casts from an enum type to an integral type that will definitely truncate the value. It is in the suspicious group and warns by default.
What you see
warning: casting `main::E::X` to `u8` will truncate the value --> main.rs:4:9 | 4 | let _ = E::X as u8; | ^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#cast_enum_truncation = note: `#[warn(clippy::cast_enum_truncation)]` 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?
The resulting integral value will not match the value of the variant it came from.
Code that is most likely wrong or useless. Warns by default.
How to fix it
Clippy does not fix this one automatically. Change the code by hand:
Flagged
enum E { X = 256 };
let _ = E::X as u8;
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::cast_enum_truncation)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
cast_enum_truncation = "allow"One run
cargo clippy -- -A clippy::cast-enum-truncationThe [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.
Clippy's own documentation
What it does
Checks for casts from an enum type to an integral type that will definitely truncate the value.
Why is this bad?
The resulting integral value will not match the value of the variant it came from.
Example
enum E { X = 256 };
let _ = E::X as u8;
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- by_ref_peekable_peekcalling `.by_ref().peekable().peek()` will advance the underlying iterator and consume its first output
- cast_abs_to_unsignedcasting the result of `i32::abs()` to u32
- cast_enum_constructorcast of an enum tuple constructor to an integer
- cast_nan_to_intcasting a known NaN to u64
- cast_slice_from_raw_partsChecks for a raw slice being cast to a slice pointer
- confusing_method_to_numeric_castcasting function pointer `u16::max` to `usize`
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::by_ref_peekable_peekcalling `.by_ref().peekable().peek()` will advance the underlying iterator and consume its first outputRead it next →Did this answer your question?