c++ - Result from operator+ to be floating-point if either lhs or rhs object is floating-point -

so have written simple template class stores array. i'm trying overload + operator sums 2 objects' arrays element element. works fine, here problem.

i want if either lhs or rhs (or both) object of floating-point type, result floating-point object.

for example: testclass({1, 2, 3}) + testclass({2.2, 3.3, 1.1}) return testclass<double> object.

i managed work if rhs object double, can't right when lhs double.

this code have written far:

#include <iostream> #include <initializer_list>  template<class t> class testclass { public:     t data[4]; public:     testclass() {}      testclass(const std::initializer_list<t> &ilist)     {         short = 0;         (const t &el : ilist) this->data[i++] = el;     }      auto &operator[](const short &i) { return this->data[i]; }      //so when called return object same     //type rhs object     template<class type_t>     auto operator+(const testclass<type_t> &rhs)     {         testclass<type_t> ret;         (short = 0; < 4; ++i)             ret.data[i] = this->data[i] + rhs.data[i];         return ret;     }  };  int main() {     testclass<int> obj = { 1, 2, 3, 4 };     testclass<double> obj2 = { 1.1, 2.2, 3.3, 4.4 };      auto res = obj2 + obj;      (short = 0; < 4; ++i)          std::cout << res[i] << " ";      std::cin.get(); } 

use decltype check type of expression:

testclass<decltype(this->data[0] + rhs.data[0])> ret;