Clippy lint · Nursery · checked with Clippy 0.1.99

clippy::unused_peekable: `peek` never called on `Peekable` iterator

What it meansChecks for the creation of a peekable iterator that is never .peek()ed It is in the nursery group and off by default.

What you see

warning: `peek` never called on `Peekable` iterator
 --> main.rs:4:5
  |
4 | let iter = collection.iter().peekable();
  |     ^^^^
  |
  = help: consider removing the call to `peekable`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unused_peekable
  = note: `-W clippy::unused-peekable` implied by `-W clippy::nursery`

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?

Creating a peekable iterator without using any of its methods is likely a mistake, or just a leftover after a refactor.

New lints still being finished. Off by default and may have false positives.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

let collection = vec![1, 2, 3];
let iter = collection.iter().peekable();

for item in iter {
    // ...
}

Write this instead

let collection = vec![1, 2, 3];
let iter = collection.iter();

for item in iter {
    // ...
}

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]
unused_peekable = "warn"

In code

#![warn(clippy::unused_peekable)]

One run

cargo clippy -- -W clippy::unused-peekable

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.

Nurserygroup

allowdefault level

nofixed by cargo clippy --fix

1.65.0added in Rust

Clippy's own documentation

What it does

Checks for the creation of a peekable iterator that is never .peek()ed

Why is this bad?

Creating a peekable iterator without using any of its methods is likely a mistake, or just a leftover after a refactor.

Example

let collection = vec![1, 2, 3];
let iter = collection.iter().peekable();

for item in iter {
    // ...
}

Use instead:

let collection = vec![1, 2, 3];
let iter = collection.iter();

for item in iter {
    // ...
}

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

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