Фрагменты Rust-овского кода, найденные в ЖЖ theiced-а.

//
// Оригинальный код
//
pub fn format_duration(duration: Duration) -> String {
    let total_seconds = duration.as_secs();

    let hours = total_seconds / 3600;
    let minutes = (total_seconds % 3600) / 60;
    let seconds = total_seconds % 60;

    let hours_label = match hours {
        1 => "hour",
        _ => "hours"
    };

    let minutes_label = match minutes {
        1 => "minute",
        _ => "minutes"
    };

    let seconds_label = match seconds {
        1 => "second",
        _ => "seconds"
    };

    let mut text = String::new();

    if hours > 0 {
        push_value_and_label(&mut text, hours, hours_label);
    }

    if minutes > 0 {
        if !text.is_empty() {
            text.push(' ');
        }

        push_value_and_label(&mut text, minutes, minutes_label);
    }

    if !text.is_empty() {
        text.push(' ');
    }

    push_value_and_label(&mut text, seconds, seconds_label);

    text
}

fn push_value_and_label(text: &mut String, value: u64, label: &str) {
    write!(text, "{} {}", value, label).unwrap();
}

//
// Предложенный альтернативный вариант
//
fn summon_satan(seconds: u64) -> String {
    let labels = vec!["hour", "minute", "second"];
    let parts = vec![seconds / 3600, (seconds % 3600) / 60, seconds % 60];
    let index = parts.iter().position(|&p| p != 0).unwrap_or(2);
    let parts_n_labels = parts[index..].iter().zip(labels[index..].iter());
    let strs = parts_n_labels.map(|(&part, &label)| format!("{} {}{}", part, label, if part == 1 { "" } else { "s" }));
    return strs.collect::<Vec<String>>().join(" ");
}

// Источники:
// https://theiced.livejournal.com/499970.html
// https://theiced.livejournal.com/500541.html