struct St {
mut:
    x f64
}

fn (s &St) get_f64() f64 {
    return s.x
}

struct Gen {
    s shared St
}

fn (g &Gen) set_val() bool {
    lock g.s {
        g.s.x = 6.25
        if g.s.x == 6.25 {
            return true
        }
        g.s.x == 7.125
    }
    return false
}

fn (g &Gen) inc_val() {
    shared q := St{
        x: 1.0
    }
    shared v := St{
        x: 0.25
    }
    lock q, g.s, v {
        g.s.x += q.x
        g.s.x += v.x
    }
}

fn test_lock_selector_expression() {
    g := Gen{
        s: St{
            x: 12.5
        }
    }
    g.set_val()
    g.inc_val()
    a := rlock g.s {
        g.s.get_f64()
    }
    assert a == 7.5
}