interface Str {
    str() string
}

struct St {}

fn (s St) str() string {
    return 's'
}

fn printer(s Str) string {
    println(s)
    return '${s}'
}

fn test_interface_str_method() {
    s := St{}
    ret := printer(s)
    assert ret == 's'
}

// for test interface gen to string
interface Abc {}

struct Xyz {}

fn test_interface_gen_to_string() {
    d := Abc(Xyz{})
    mut res := ''
    if d is Xyz {
        println(d)
        res = '${d}'
    }
    assert res == '&Xyz{}'
}