OptionalIndex

    pub const OptionalIndex = enum(u32) {
        none = max_u32 - 1,
        root = max_u32,
        _,

        pub fn init(i: Index) OptionalIndex {
            const result: OptionalIndex = @fromBackingInt(@intCast(@backingInt(i)));
            assert(result != .none);
            return result;
        }

        pub fn unwrap(this: @This()) ?Index {
            return switch (this) {
                .none => null,
                .root => .root,
                _ => @fromBackingInt(@intCast(@backingInt(this))),
            };
        }
    }