pub struct Base {
mut:
    x int
    y int
}

pub fn (mut b Base) init() {}

pub fn (b Base) get_pos() (int, int) {
    return b.x, b.y
}

pub struct Label {
    Base
}

pub interface Widget {
mut:
    init()
}

pub interface Layoutable {
    get_pos() (int, int)
}

pub struct Layout {
    Base
mut:
    widgets []Widget
}

pub fn (mut l Layout) layout() {
    for wd in l.widgets {
        if wd is Layoutable {
            lw := wd as Layoutable
            dump(lw.get_pos())
            x, y := lw.get_pos()
            assert x == 10
            assert y == 20
        } else {
            println('wd is NOT Layoutable')
        }
    }
}

fn test_struct_embed_is_interface() {
    mut l := Layout{}
    l.widgets << Label{
        x: 10
        y: 20
    }
    l.layout()
}