Clippy lints / Correctness
Clippy lint · Correctness · checked with Clippy 0.1.99
clippy::approx_constant: approximate value of `f{32, 64}::consts::PI` found
What it meansChecks for floating point literals that approximate constants which are defined in std::f32::consts or std::f64::consts, respectively, suggesting to use the predefined constant. It is in the correctness group and denied by default (the build fails).
What you see
error: approximate value of `f{32, 64}::consts::PI` found --> main.rs:3:9 | 3 | let x = 3.14; | ^^^^ | = help: consider using the constant directly = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#approx_constant = note: `#[deny(clippy::approx_constant)]` 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?
Usually, the definition in the standard library is more precise than what people come up with. If you find that your definition is actually more precise, please file a Rust issue.
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
let x = 3.14;
let y = 1_f64 / x;
Write this instead
let x = std::f32::consts::PI;
let y = std::f64::consts::FRAC_1_PI;
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::approx_constant)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
approx_constant = "allow"One run
cargo clippy -- -A clippy::approx-constantThe [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 floating point literals that approximate
constants which are defined in
std::f32::consts
or
std::f64::consts,
respectively, suggesting to use the predefined constant.
Why is this bad?
Usually, the definition in the standard library is more precise than what people come up with. If you find that your definition is actually more precise, please file a Rust issue.
Example
let x = 3.14;
let y = 1_f64 / x;
Use instead:
let x = std::f32::consts::PI;
let y = std::f64::consts::FRAC_1_PI;
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.
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All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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