FOR_LOOPS_OVER_FALLIBLES in rustc_lint::for_loops_over_fallibles - Rust
Description: The `for_loops_over_fallibles` lint checks for `for` loops over `Option` or `Result` values.

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## FOR_LOOPS_OVER_FALLIBLES

# Static FOR_LOOPS_OVER_FALLIBLES

Source

    pub static FOR_LOOPS_OVER_FALLIBLES: &Lint

Expand description

The `for_loops_over_fallibles` lint checks for `for` loops over `Option` or `Result` values.

#### §Example

    let opt = Some(1);
    for x in opt { /* ... */}

{{produces}}

#### §Explanation

Both `Option` and `Result` implement `IntoIterator` trait, which allows using them in a `for` loop. `for` loop over `Option` or `Result` will iterate either 0 (if the value is `None`/`Err(_)`) or 1 time (if the value is `Some(_)`/`Ok(_)`). This is not very useful and is more clearly expressed via `if let`.

`for` loop can also be accidentally written with the intention to call a function multiple times, while the function returns `Some(_)`, in these cases `while let` loop should be used instead.

The “intended” use of `IntoIterator` implementations for `Option` and `Result` is passing them to generic code that expects something implementing `IntoIterator`. For example using `.chain(option)` to optionally add a value to an iterator.