Why memory leak here after operator<< call? Without operator<< everything is okey:
#include <cstdlib>
#include <cstring>

class String
{
public:
    String(const char* str) : size(strlen(str)), str(new char[size + 1])
    {
        for (uint32_t ch = 0; ch != size; ++ch)
        {
            this->str[ch] = str[ch];
        }
        this->str[size] = '\0';
    }

    ~String()
    {
        delete[] str;
    }

    int size;
    char* str;

    friend std::ostream& operator<<(std::ostream& cout, const String & s);
};

std::ostream& operator<<(std::ostream& cout, const String & s)
{
    cout << s.str << "\n";

    return cout;
}

int main()
{
    String s1("hello");
    std::cout << s1;

    return 0;
 }