#include <stdexcept>
#include <iostream>
 
template <typename T>
struct fibonacci_sequence
{
    using value_type = T;
 
    value_type operator()()
    {
        if (next < current)
            throw std::overflow_error("Overflow encountered in fibonacci_sequence.");
 
        auto result = current;
 
        auto next_in_series = current + next;
        current = next;
        next = next_in_series;
 
        return result;
    }
 
 
private:
    value_type current = 0;
    value_type next = 1;
};
 
template <typename sequence>
void largest_generated(sequence& seq)
{
    typename sequence::value_type largest = 0;
 
    try {
        for (;;)
            largest = seq();
    }
 
    catch (std::exception& ex)
    {
        std::cout << ex.what() << '\n';
        std::cout << "Last value generated was " << largest << "\n\n";
    }
}
 
int main()
{
    fibonacci_sequence<int> int_seq;
    fibonacci_sequence<unsigned> unsigned_seq;
    fibonacci_sequence<unsigned long long> ull_seq;
 
    largest_generated(int_seq);
    largest_generated(unsigned_seq);
    largest_generated(ull_seq);
}

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