Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::duration_suboptimal_units: constructing a `Duration` using a smaller unit when a larger unit would be more readable

What it meansChecks for instances where a std::time::Duration is constructed using a smaller time unit when the value could be expressed more clearly using a larger unit. For literal values that would convert to 10 or fewer of the larger unit, this lint does not apply. It is in the pedantic group and off by default.

What you see

warning: constructing a `Duration` using a smaller unit when a larger unit would be more readable
 --> main.rs:5:11
  |
5 | let dur = Duration::from_millis(50_000);
  |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#duration_suboptimal_units
  = note: `-W clippy::duration-suboptimal-units` implied by `-W clippy::pedantic`
help: try using `Duration::from_secs`
  |
5 - let dur = Duration::from_millis(50_000);
5 + let dur = Duration::from_secs(50);
  |

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?

Using a smaller unit for a duration that is evenly divisible by a larger unit reduces readability. Readers have to mentally convert values, which can be error-prone and makes the code less clear.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

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

use std::time::Duration;

let dur = Duration::from_millis(50_000);
let dur = Duration::from_secs(1800);
let dur = Duration::from_mins(10 * 60);

Write this instead

use std::time::Duration;

let dur = Duration::from_secs(50);
let dur = Duration::from_mins(30);
let dur = Duration::from_hours(10);

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
duration_suboptimal_units = "warn"

In code

#![warn(clippy::duration_suboptimal_units)]

One run

cargo clippy -- -W clippy::duration-suboptimal-units

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.

Pedanticgroup

allowdefault level

yesfixed by cargo clippy --fix

1.95.0added in Rust

Clippy's own documentation

What it does

Checks for instances where a std::time::Duration is constructed using a smaller time unit when the value could be expressed more clearly using a larger unit.

For literal values that would convert to 10 or fewer of the larger unit, this lint does not apply.

Why is this bad?

Using a smaller unit for a duration that is evenly divisible by a larger unit reduces readability. Readers have to mentally convert values, which can be error-prone and makes the code less clear.

Example

use std::time::Duration;

let dur = Duration::from_millis(50_000);
let dur = Duration::from_secs(1800);
let dur = Duration::from_mins(10 * 60);

Use instead:

use std::time::Duration;

let dur = Duration::from_secs(50);
let dur = Duration::from_mins(30);
let dur = Duration::from_hours(10);

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

Up next

Also worth your time

Did this answer your question?