clippy::redundant_closure_call: try not to call a closure in the expression where it is declared

What you see

warning: try not to call a closure in the expression where it is declared
 --> main.rs:3:9
  |
3 | let a = (|| 42)();
  |         ^^^^^^^^^ help: try doing something like: `42`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#redundant_closure_call
  = note: `#[warn(clippy::redundant_closure_call)]` 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 is unnecessarily adding to the expression’s complexity.

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 a = (|| 42)();

Write this instead

let a = 42;

Turn it off, or on

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

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

[lints.clippy]
redundant_closure_call = "allow"

cargo clippy -- -A clippy::redundant-closure-call

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.