Реализация макросов для разбора строк по префиксам с детекцией повторяющихся паттернов

main.rs

macro_rules! prefixes {
    (match $value:ident {
        $($prefix:literal .. $(if $condition:expr)? => $arm:expr,)*
        _ => $catch_all:expr $(,)?
    }) => {{
        #[allow(dead_code)]
        fn non_repeating() {
            #[warn(unreachable_patterns)]
            match "" {
                $($prefix => (),)*
                _ => (),
            }
        }
        match $value {
            $(x if x.starts_with($prefix) $(&& $condition)? => $arm,)*
            _ => $catch_all,
        }
    }}
}

macro_rules! cut_prefixes {
    (match $value:ident {
        $($prefix:literal..=$rest:ident => $arm:expr,)*
        _ => $catch_all:expr $(,)?
    }) => {{
        #[allow(dead_code)]
        fn non_repeating() {
            #[warn(unreachable_patterns)]
            match "" {
                $($prefix => (),)*
                _ => (),
            }
        }
        $(if let Some($rest) = $value.strip_prefix($prefix) {
            $arm
        } else)* {
            $catch_all
        }
    }}
}

fn use_cut_prefixes(s: &str) -> String {
    cut_prefixes!(match s {
        "foo"..=rest => rest.to_string(),
        "bar"..=tail /* if s.len() % 2 == 0 */ => [tail, tail].concat(),
        _ => String::new(),
    })
}

fn use_prefixes(s: &str) -> String {
    prefixes!(match s {
        "foo".. => s.to_string(),
        "bar".. => [s, s].concat(),
        "over".. if s.ends_with("all") => [s, "3"].concat(),
        _ => String::new(),
    })
}

fn main() {
    let inputs = [
        "foobar",
        "barfoo",
        "overall",
    ];

    for input in &inputs[..] {
        println!("{:?}", use_prefixes(input));
    }
}

// версия cut_prefixes с поддержкой if clause
/*
macro_rules! cut_prefixes {
    (match $value:ident {
        $($prefix:literal..=$rest:ident $(if $cond:expr)? => $arm:expr,)*
        _ => $catch_all:expr $(,)?
    }) => {{
        #[allow(dead_code)]
        fn non_repeating() {
            #[warn(unreachable_patterns)]
            match "" {
                $($prefix => (),)*
                _ => (),
            }
        }
        match $value {
            $(x if x.starts_with($prefix) $(&& $cond)? => {
                let (_, $rest) = x.split_at($prefix.len());
                $arm
            },)*
            _ => $catch_all,
        }
    }}
}
*/

Пост: https://t.me/dereference_pointer_there/1366