macro to optimize chrono DateTime formatting by lazilly parsing format string and memoization/interning of the result

chrono_format_parsed_and_interned.rs

use std::sync::OnceLock;
use chrono::{DateTime, Utc, format::StrftimeItems};

pub fn format_date(ts: DateTime<Utc>) -> String {
    static FORMAT: OnceLock<Vec<chrono::format::Item<'static>>> = OnceLock::new();
    let items = FORMAT.get_or_init(|| StrftimeItems::new("%Y-%m-%d").collect());
    ts.format_with_items(items.iter()).to_string()
}

/// Creates functions like the one above
macro_rules! def_time_formatting_func {
    ($name:ident, $format_str:expr) => {
        pub fn $name(ts: chrono::DateTime<chrono::Utc>) -> String {
            static FORMAT: std::sync::OnceLock<Vec<chrono::format::Item<'static>>> = std::sync::OnceLock::new();
            let items = FORMAT.get_or_init(|| chrono::format::StrftimeItems::new($format_str).collect());
            ts.format_with_items(items.iter()).to_string()
        }
    };
}

def_time_formatting_func!(format_iso, "%Y-%m-%dT%H:%M:%S%z");
def_time_formatting_func!(format_pretty, "%Y-%m-%d %_H:%M");