Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::unnecessary_cast: casting integer literal to `i32` is unnecessary

What it meansChecks for casts to the same type, casts of int literals to integer types, casts of float literals to float types, and casts between raw pointers that don’t change type or constness. It is in the complexity group and warns by default.

What you see

warning: casting integer literal to `i32` is unnecessary
 --> main.rs:3:9
  |
3 | let _ = 2i32 as i32;
  |         ^^^^^^^^^^^ help: try: `2_i32`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unnecessary_cast
  = note: `#[warn(clippy::unnecessary_cast)]` 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?

It’s just unnecessary.

Code that does something simple in a complicated way. 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 _ = 2i32 as i32;
let _ = 0.5 as f32;

Write this instead

let _ = 2_i32;
let _ = 0.5_f32;

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::unnecessary_cast)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
unnecessary_cast = "allow"

One run

cargo clippy -- -A clippy::unnecessary-cast

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.

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for casts to the same type, casts of int literals to integer types, casts of float literals to float types, and casts between raw pointers that don’t change type or constness.

Why is this bad?

It’s just unnecessary.

Known problems

When the expression on the left is a function call, the lint considers the return type to be a type alias if it’s aliased through a use statement (like use std::io::Result as IoResult). It will not lint such cases.

This check will only work on primitive types without any intermediate references: raw pointers and trait objects may or may not work.

Example

let _ = 2i32 as i32;
let _ = 0.5 as f32;

Better:

let _ = 2_i32;
let _ = 0.5_f32;

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

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