Match on i32 - function call in pattern

[Jesper]

With

let c: i32 =ncurses::getch();

we can do

if c=='q' as i32  {
}

but not

match c {
    'q' as i32 => (),
    _
}

instead we can do

match c {
    113  => (),
    _
}

Is there another way of handling this in match statement?
Function calls are not allowed in patterns...

[steffahn]

Constants are allowed as patterns.

While eventually, once we get that feature, something like const { 'q' as i32 } should work, you can define a constant like

const LOWER_Q_CODE: i32 = 'q' as i32;

and use it as a pattern. For this, it's useful that items such as const are also allowed to be defined locally, e. g. within a function, so you can keep it close to where it's used and the visibility limited.

Rust Playground

[kiyov09]

Maybe the pattern gets a little longer but you can do:

match c {
    _ if c=='q' as i32 => (),
    _
}

[Heliozoa]

It's a little more verbose because you need two conversions which are both fallible, but you could try to convert the input into a char for the match

match u32::try_from(c).ok().and_then(char::from_u32) {
    Some('c') => {}
    _ => {}
}

[scottmcm]

@Heliozoa

because you need two conversions which are both fallible

Unicode Scalar Values are always small enough that it would be fine to write this as

match char::from_u32(c as u32) {

but

@Jesper

let c: i32 =ncurses::getch();

based on https://manpages.debian.org/bullseye/ncurses-doc/getch.3ncurses.en.html, that's not actually returning unicode in the first place, so going via char at all is probably wrong -- KEY_RESIZE is not a unicode character.

Since it mentions

The *get* functions are described in the XSI Curses standard, Issue 4. They read single-byte characters only.

then maybe you'd like

    match c.try_into() {
        Ok(b'q') => …,
        _ => …,
    }

Or I guess you could try a different version of ncurses, and use getch in ncursesw - Rust which seems to be able to give back chars.