How to set the guard for specified pattern?

[Zaplae]

Code:

pub fn handle_keys(event: KeyEvent, app: &mut App) {
    match event.code {
        KeyCode::Char('q') | KeyCode::Char('c') if KeyModifiers::CONTROL == event.modifiers => {
            app.is_running = false
        }
        _ => {}
    }
}

The if takes effect for all patterns.

Are there any way could do the same thing like the following code?

    match event.code {
        KeyCode::Char('q') | (KeyCode::Char('c') if KeyModifiers::CONTROL) == event.modifiers => {
            app.is_running = false
        }
        _ => {}
    }

I don't want to use the following code, because app.is_running is repeated.

    match event.code {
        KeyCode::Char('q') => app.is_running = false,
        KeyCode::Char('c') if KeyModifiers::CONTROL == event.modifiers => app.is_running = false,
        _ => {}
    }

[LegionMammal978]

The syntax as written can't work, since an if condition guard is part of the match arm, not part of the pattern. The closest equivalent I could think of would be to repeat the checks in the guard:

match event.code {
    KeyCode::Char('q') | KeyCode::Char('c')
        if event.code == KeyCode::Char('q') || event.modifiers == KeyModifiers::CONTROL =>
    {
        app.is_running = false;
    }
    _ => {}
}

If the alternative is simply to do nothing when the arm doesn't match, an early return would work (this could be written as either an if or a nested match):

match event.code {
    KeyCode::Char('q') | KeyCode::Char('c') => {
        if event.code == KeyCode::Char('c') || event.modifiers != KeyModifiers::CONTROL {
            return;
        }
        app.is_running = false;
    }
    _ => {}
}

But in general, if the body is not very long, I'd be inclined to repeat it, as in your last example.

[memark]

Your first two code snippets are identical (no?), so I'm not sure what it is you're trying to achieve. Could you elaborate?

[steffahn]

There’s unfortunately no way of applying a guard just to a part of an or pattern. In your particular code example, I would probably write something like

if matches!(event.code, KeyCode::char('q))
    || matches!(event.code, KeyCode::Char('c) if event.modifiers == KeyModifiers::CONTROL)
{
    app.is_running = false
}

You could also try to use pattern matching instead of == for the .modifiers (not 100% sure if that works though for that type)… perhaps even matching on the whole event:

match event {
    KeyEvent {
        code: KeyCode::Char('q'),
        ..
    }
    | KeyEvent {
        code: KeyCode::Char('c'),
        modifiers: KeyModifiers::CONTROL,
        ..
    } => app.is_running = false,
    _ => {}
}

hm… that turns out a bit lengthy with standard rustfmt; without it you can remove some line breaks if you prefer that

match event {
    KeyEvent { code: KeyCode::Char('q'), .. }
    | KeyEvent { code: KeyCode::Char('c'), modifiers: KeyModifiers::CONTROL, .. } => {
        app.is_running = false
    }
    _ => {}
}

[cuviper]

You could move the character test:

    KeyCode::Char(ch) if ch == 'q' || ch == 'c' && ...