RS.CLIPPY.MANUAL_TRY_FOLD

Checks for usage of `Iterator::fold` with a type that implements `Try`

This checker is a Clippy lint created by The Rust Project Contributors. The documentation shown here is a copy of the original documentation for: manual_try_fold. Copyright ©2025 The Rust Team. All rights reserved.

What it does

Checks for usage of Iterator::fold with a type that implements Try.

Why is this bad?

The code should use try_fold instead, which short-circuits on failure, thus opening the door for additional optimizations not possible with fold as rustc can guarantee the function is never called on None, Err, etc., alleviating otherwise necessary checks. It's also slightly more idiomatic.

Known issues

This lint doesn't take into account whether a function does something on the failure case, i.e., whether short-circuiting will affect behavior. Refactoring to try_fold is not desirable in those cases.

Example

vec![1, 2, 3].iter().fold(Some(0i32), |sum, i| sum?.checked_add(*i));

Use instead:

vec![1, 2, 3].iter().try_fold(0i32, |sum, i| sum.checked_add(*i));

Configuration

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

(default: current version)