无限数组C++在一个表达式中使用两个新值调整数组大小

我已经开始使用C++中的模板实现无限数组。除了在一个表达式中添加两个新项的特殊情况外，添加整数效果很好，这需要一个接一个地调整两个大小(参见下文)。

#include <iostream>
#include <cstddef>
#include <new>
#include <string.h>
template <typename T>
struct infinite_array {
infinite_array();
auto operator[](unsigned long long idx) -> T&;
auto size() const -> unsigned long long;
void resize(unsigned long long idx);
private:
T *data;
unsigned long long array_length;
};
template <typename T>
void infinite_array<T>::resize(unsigned long long idx)
{
std::cout << "Resize with idx " << idx << std::endl;
T* temp = new T[idx];
memset(temp, 0, sizeof(T) * idx);
for (int i = 0; i < array_length; ++i) {
temp[i] = data[i];
std::cout <<  temp[i] << " ";
}
std::cout << std::endl; 
//std::copy(data, data+size(), temp);
delete [] data;
data = temp;
array_length = idx;
}
template <typename T>
infinite_array<T>::infinite_array() 
{
data = NULL;
array_length = 0;
}
template <typename T>
auto infinite_array<T>::size() const -> unsigned long long {
//array_length = sizeof(data)/sizeof(T);
return array_length;
}
template <typename T>
auto infinite_array<T>::operator[](unsigned long long idx) -> T& {
//std::cout << "Accessing element at idx " << idx << std::endl;
if (idx+1 > size()) {
resize(idx+1);  
}
return data[idx];
}
int main() {
infinite_array<int> ar; 
for (int i = 0; i < 10; ++i) {
ar[i] = i;
}
// PROBLEM: ONLY ar[31] is initialized successfully to 10
ar[30] = ar[31] = 10;
for (int i = 0; i < ar.size(); ++i)
std::cout << ar[i] << ' ';  
std::cout << std::endl;
return 0;
}