Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::excessive_precision: float has excessive precision
What it meansChecks for float literals with a precision greater than that supported by the underlying type. The lint is suppressed for literals with over const_literal_digits_threshold digits. It is in the style group and warns by default.
What you see
warning: float has excessive precision --> main.rs:3:14 | 3 | let v: f32 = 0.123_456_789_9; | ^^^^^^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#excessive_precision = note: `#[warn(clippy::excessive_precision)]` on by default help: consider changing the type or truncating it to | 3 - let v: f32 = 0.123_456_789_9; 3 + let v: f32 = 0.123_456_79; |
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?
Rust will truncate the literal silently.
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
let v: f32 = 0.123_456_789_9;
println!("{}", v); // 0.123_456_789
Write this instead
let v: f64 = 0.123_456_789_9;
println!("{}", v); // 0.123_456_789_9
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::excessive_precision)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
excessive_precision = "allow"One run
cargo clippy -- -A clippy::excessive-precisionThe [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
const-literal-digits-threshold: The minimum digits a const float literal must have to supress the excessive_precicion lint
Clippy's own documentation
What it does
Checks for float literals with a precision greater than that supported by the underlying type.
The lint is suppressed for literals with over const_literal_digits_threshold digits.
Why is this bad?
Rust will truncate the literal silently.
Example
let v: f32 = 0.123_456_789_9;
println!("{}", v); // 0.123_456_789
Use instead:
let v: f64 = 0.123_456_789_9;
println!("{}", v); // 0.123_456_789_9
Configuration
-
const-literal-digits-threshold: The minimum digits a const float literal must have to supress theexcessive_precicionlint(default:
30)
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
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- duplicate_underscore_argument`a` already exists, having another argument having almost the same name makes code comprehension and documentation more difficult
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- err_expectcalled `.err().expect()` on a `Result` value
- field_reassign_with_defaultChecks for immediate reassignment of fields initialized with Default::default()
- filter_map_bool_thenChecks for usage of bool::then in Iterator::filter_map
- fn_to_numeric_castcasting function pointer `fun` to `i64`
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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