You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: helpers.rs
    path of file: ./repos/icu4x/components/datetime/src/pattern/runtime
    
    the code of the file until where you have to start completion: // This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use super::{super::PatternItem, Pattern};
use zerovec::ule::AsULE;

/// Helper function which takes a runtime `Pattern` and calls
/// the callback function passing each item until the callback
/// returns a new value.
///
/// When that happens, the `Pattern` is turned into an owned one,
/// and the old item gets replaced with the new one.
///
/// The utility of th
    
pub fn maybe_replace(pattern: &mut Pattern, f: impl Fn(&PatternItem) -> Option<PatternItem>) {
    let result = pattern
        .items
        .iter()
        .enumerate()
        .find_map(|(i, item)| f(&item).map(|result| (i, result)));
    #[allow(clippy::indexing_slicing)] // i was produced by enumerate
    if let Some((i, result)) = result {
        let owned = pattern.items.to_mut_slice();
        owned[i] = result.to_unaligned();
        owned.iter_mut().skip(i).for_each(|item| {
            if let Some(new_item) = f(&PatternItem::from_unaligned(*item)) {
                *item = new_item.to_unaligned();
            }
        });
    }
}