Macro on_gained 

macro_rules! on_gained {
    ($($field:expr => $validate:expr),*) => { ... };
}

Does a match on the state struct of a widget. If widget_state.gained_focus() is true the block is executed. This requires that widget_state implements HasFocus, but that’s the basic requirement for this whole crate.

use rat_focus::on_gained;

on_gained!(
    state.field1 => {
        // do prep
    },
    state.field2 => {
        // do prep
    }
);