I've been reading Item 6 from Scott Meyers' Effective Modern C++ and noticed he mentioned a technique called "expression templates". I've decided to give it a try and implemented a vector that supports addition and subtraction:

#include <iostream>
#include <vector>

template<typename T>
class Vec
{
public:
    std::vector<T> data;

    typedef typename std::vector<T>::size_type size_type;
    
    Vec(size_type size): data(size)
    {
    }

    Vec(const std::initializer_list<T>& elements): data(elements.size())
    {
        size_type i = 0;
        for (const auto& el: elements)
        {
            data[i++] = el;
        }
    }

    template<typename VecOperation>
    Vec(const VecOperation& vo): data(vo.t2.data.size())
    {
        for (size_type i = 0; i < data.size(); ++i)
        {
            data[i] = vo[i];
        }
    }

    T operator[](size_type i) const
    {
        return data[i];
    }
};

template<typename T1, typename T2>
struct VecSum
{
    const T1& t1;
    const T2& t2;
    auto operator[](typename T2::size_type i) const
    {
        return t1[i] + t2[i];
    }
};

template<typename T1, typename T2>
struct VecDiff
{
    const T1& t1;
    const T2& t2;
    auto operator[](typename T2::size_type i) const
    {
        return t1[i] - t2[i];
    }
};

template<typename T1, typename T2>
auto operator+(const T1& t1, const T2& t2)
{
    return VecSum<T1, T2>{t1, t2};
}

template<typename T1, typename T2>
auto operator-(const T1& t1, const T2& t2)
{
    return VecDiff<T1, T2>{t1, t2};
}

int main()
{
    Vec<int> v1{1, 2, 3, 4, 5};
    Vec<int> v2{6, 7, 8, 9, 11};
    Vec<int> v3{3, 5, 2, 0, 17};

    Vec<int> v4 = v1+v2-v3;

    for (const auto& x: v4.data)
    {
        std::cout << x << ", ";
    }
    std::cout << std::endl;

    return 0;
}

The main advantage of this solution is that in the line Vec<int> v4 = v1+v2-v3; no additional temporaries of type Vec are created which increases performance.

I'd be grateful if someone could point potential drawbacks and possible further improvements of this code.