interface ObjectCollection<+T as object> extends IteratorAggregate<int, T> {}

function foo(): vec<int> {
    return vec[1, 2, 3];
}

function bar(): dict<string, int> {
    return dict['a' => 1, 'b' => 2, 'c' => 3];
}

function baz(bool $a): iterable<int, int> {
    if $a {
        return vec[1, 2, 3];
    } else {
        return dict[1 => 1, 2 => 2, 3 => 3];
    }
}

final class Box<T> {
    public function __construct(public T $value) {}
}

function box(): Box<vec<int>> {
    return new Box(vec[1, 2, 3]);
}

function unbox(Box<vec<int>> $box): vec<int> {
    return $box->value;
}

function foo(bool $a, bool $b): vec<int>|dict<string, int>|Box<vec<int>> {
    if $a {
        return vec[1, 2, 3];
    } else if $b {
        return dict['a' => 1, 'b' => 2, 'c' => 3];
    } else {
        return new Box(vec[1, 2, 3]);
    }
}

function into_vec<T>(iterable<_, Tv> $iterable): vec<T> {
    $vec = vec[];
    foreach $iterable as $value {
        $vec[] = $value;
    }

    return $vec;
}

function into_dict<Tk, Tv>(iterable<Tk, Tv> $iterable): dict<Tk, Tv> {
    $dict = dict[];
    foreach $iterable as $key => $value {
        $dict[$key] = $value;
    }

    return $dict;
}

function baz(): void {
    $dict = dict[1 => 1, 2 => 2, 3 => 3];
    $vec = vec[1, 2, 3];

    $dict2 = into_dict::<int, int>($vec);
    $vec2 = into_vec::<int>($dict);

    $a = vec[$dict1, $dict2];
    $b = into_dict::<int, dict<int, int>>($a);

    $c = new Box::<dict<int, dict<int, int>>>($b);
}