Expression must have class type, but has type

Question

I have error Expression must have class type, but has type at assert(n == array1.size());

#include <iostream>
#include "Array.h"
#include <cassert>

using namespace std;

int main()
{
    const size_t n = 4;
    Array<n, int> array1();
    assert(array1.size() == n);
}

And this is class Array with size() :

template <size_t n, typename T>
class Array {
private:
    const size_t _size;
    T* const _allocator;
//...
public:
    Array();
    ~Array();
//...
    size_t size() const;
};