fn f(n int) ?int {
    if n < 0 {
        return none
    }
    return n
}

fn test_lhs_option() {
    mut a := [0, 1, 2, 3, 4]
    a[f(-1) or { 2 }] = 7
    assert a == [0, 1, 7, 3, 4]
}

fn ret_no_opt(n int) int {
    return f(n) or { panic(err) }
}

fn test_opt_return_no_opt() {
    aa := ret_no_opt(3)
    assert aa == 3
}

fn test_range_for_and_array_push() {
    mut a := []int{}
    for n in f(-3) or { -1 } .. f(3) or { 12 } {
        a << f(n) or { -5 }
    }
    assert a == [-5, 0, 1, 2]
}

fn test_channel_push() {
    ch := chan f64{cap: 2}
    ch <- 12.25
    ch.close()
    mut res := []f64{cap: 3}
    for _ in 0 .. 3 {
        res << <-ch or { -6.75 }
    }
    assert res == [12.25, -6.75, -6.75]
}

fn test_thread_wait() {
    thrs := [
        spawn f(3),
        spawn f(-7),
        spawn f(12),
    ]
    mut res := []int{cap: 3}
    for t in thrs {
        res << t.wait() or { -13 }
    }
    assert res == [3, -13, 12]
}

fn test_nested_opt() {
    a := f(f(f(-3) or { -7 }) or { 4 }) or { 17 }
    assert a == 4
}

fn foo() ?string {
    return 'hi'
}

fn test_opt_subexp_field() {
    assert foo()?.len == 2
}

fn test_mut_opt_none_if_branch() {
    mut x := ?int(none)

    if x != none {
        x = 10
    } else {
        x = 5
    }
    assert x? == 5
}