Template with auto-type return deduction

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Category:Languages

I have created a templated struct and am trying to overload the binary operators. For some reason the function does not return the correct data type even though the type is correctly casted in between.

template<typename T> struct Number{     const T value;     Number(T a) : value(a) {}      template<typename U>     auto operator*(Number<U> other){         auto new_value = value*other.value;         std::cout << typeid(new_value).name() << std::endl;         return Number(new_value);     } }; 

Now if I perform this operation with the following code called in main. It returns Number of the type of the first one, not number of the higher type.

auto b =  Number<int>(6) * Number<double>(2.3); // this should be an int*double=double std::cout << b.value << typeid(b.value).name() << std::endl; auto c = Number<double>(2.3) * Number<int>(6); std::cout << c.value << typeid(c.value).name() << std::endl; 

Output is as follows: d 13i d 13.8d

From what I understand, the incorrect constructor is called when the function return the new Number(new_value). I do not understand how and why this happens as new_value is of the 'correct type'.

 


Inside the scope of a template, the template-name is going to stand for the injected class name, and not for the template. So there will not be CTAD, and that's by design

Using return Number<decltype(new_value)>(new_value); is the simple workaround.

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