test "for basics" {
    const items = [_]i32 { 4, 5, 3, 4, 0 };
    var sum: i32 = 0;

    // For loops iterate over slices and arrays.
    for (items) |value| {
        if (value == 0) {
            continue;
        }
        sum += value;
    }
    assert(sum == 16);

    for (items[0..1]) |value| {
        sum += value;
    }
    assert(sum == 20);

    var sum2: i32 = 0;
    for (items) |value, i| {
        assert(@TypeOf(i) == usize);
        sum2 += @intCast(i32, i);
    }
    assert(sum2 == 10);
}

test "for reference" {
    var items = [_]i32 { 3, 4, 2 };

    for (items) |*value| {
        value.* += 1;
    }

    assert(items[0] == 4);
    assert(items[1] == 5);
    assert(items[2] == 3);
}

test "for else" {
    var items = [_]?i32 { 3, 4, null, 5 };

    var sum: i32 = 0;
    const result = for (items) |value| {
        if (value != null) {
            sum += value.?;
        }
    } else blk: {
        assert(sum == 12);
        break :blk sum;
    };
    assert(result == 12);
}