clippy::vec_box: `Vec<T>` is already on the heap, the boxing is unnecessary

What you see

warning: `Vec<T>` is already on the heap, the boxing is unnecessary
 --> main.rs:4:13
  |
4 |     values: Vec<Box<i32>>,
  |             ^^^^^^^^^^^^^ help: try: `Vec<i32>`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#vec_box
  = note: `#[warn(clippy::vec_box)]` 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?

Vec already keeps its contents in a separate area on the heap. So if you Box its contents, you just add another level of indirection.

Code that does something simple in a complicated way. Warns by default.

How to fix it

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

Flagged

struct X {
    values: Vec<Box<i32>>,
}

Write this instead

struct X {
    values: Vec<i32>,
}

Turn it off, or on

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

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

[lints.clippy]
vec_box = "allow"

cargo clippy -- -A clippy::vec-box

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.

Settings in clippy.toml

• avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.
• vec-box-size-threshold: The size of the boxed type in bytes, where boxing in a Vec is allowed