Size

    const Size = packed struct(usize) {
        resizing: bool,
        _: @Int(.unsigned, @bitSizeOf(usize) - 1) = 0,

        fn fromInt(int: usize) Size {
            assert(int >= @sizeOf(Node));
            const size: Size = @bitCast(int);
            assert(!size.resizing);
            return size;
        }

        fn toInt(size: Size) usize {
            var int = size;
            int.resizing = false;
            return @bitCast(int);
        }

        comptime {
            assert(Size{ .resizing = true } == @as(Size, @bitCast(@as(usize, 1))));
        }
    }