ensureTotalCapacity

        pub fn ensureTotalCapacity(self: *Self, allocator: Allocator, new_capacity: usize) !void {
            var better_capacity = self.capacity();
            if (better_capacity >= new_capacity) return;
            while (true) {
                better_capacity += better_capacity / 2 + 8;
                if (better_capacity >= new_capacity) break;
            }
            self.items = try allocator.realloc(self.items, better_capacity);
        }